Al2O3: ionic bonding F2: London dispersion forces H2O: hydrogen bonding Br2: London dispersion forces Icl: London dispersion forces and dipole-dipole interactions Nacl: ionic bonding. these are the intermolecular forces found in the molecules , order of molecules based on boiling point is Al2O3 Nacl H2O ICl F2 Br2
The intermolecular forces that predominate in a substance determine the physical properties of that substance, such as its boiling point. The relative strength of these forces is determined by the type of bond present in the substance and the polarity of the molecules. ionic bonding, as found in Al2O3 and Nacl, is the strongest type of intermolecular force. It occurs when positively and negatively charged ions are attracted to each other, forming a crystal lattice. Because of the strong electrostatic forces between the ions, substances with ionic bonding have very high melting and boiling points.Hydrogen bonding, as found in H2O, is the next strongest intermolecular force. It occurs when a hydrogen atom, covalently bonded to a highly electronegative atom (such as oxygen or nitrogen), is attracted to another electronegative atom. This creates a temporary dipole-dipole interaction, which is weaker than ionic bonding but still strong enough to give substances with hydrogen bonding high boiling points. Dipole-dipole interactions, as found in ICl, occur when polar molecules are attracted to each other. These interactions are weaker than hydrogen bonding, so substances with dipole-dipole interactions have lower boiling points.London dispersion forces, as found in F2, Br2, and ICl, are the weakest type of intermolecular force. They are temporary forces that arise due to the random motion of electrons in a molecule, causing a temporary dipole. Because they are so weak, substances with London dispersion forces have very low boiling points.
to know more about bonds-
https://brainly.com/question/15444131
#SPJ4
arrange the organic compounds from most soluble in water to least soluble in water.a. CH3CH3b. CH3OCH3c. CH3CH2OH1. most soluble in water2. least soluble in water
The organic compounds from most soluble in water to least soluble in water is CH3CH2OH, CH3CH3 and CH3OCH3.
The degree to which a substance dissolves in a solvent to form a solution is known as solubility ( expressed as grams of solute per liter of solvent). One fluid's ability to completely dissolve another fluid (liquid or gas; for example, methanol and water) or only partially do so (oil and water dissolve only slightly). "Like dissolves like," in general ( aromatic hydrocarbons dissolve in each other but not in water). According to the distribution coefficient (the ratio of a material's solubilities in two solvents), some separation techniques (such as absorption and extraction) rely on differences in solubility. In general, as temperature rises, so do the solubilities of solids in liquids, while they fall as temperature rises and rise with pressure for gases. A solution is said to be saturated when no more solute can dissolve in it at a specific temperature and pressure.
To know more about solubility visit :https://brainly.com/question/14747303
#SPJ4
what is the product of the reaction of bromoethane with each of the following nucleophiles?
1-butyne is the product that is formed by the reaction of bromoethane and the following nucleophile sodium acetylide.
Definition of nucleophilic substitution reaction
Nucleophilic substitution reactions are a class of reactions in which an electron rich nucleophile attacks a positively charged electrophile and replaces a leaving group. For alginate reactions, the most reactive nucleophile is considered as the C6 carboxylate group.
1-butyne is the product formed from the reaction between bromoethane and sodium acetylide. This reaction is a nucleophilic substitution type reaction where acetylide ion act as nucleophile. General reaction is given below:
C₂HNa + C₂H₅Br → CH₃CCHCH₂ + NaBr
1-butyne is the product formed in this reaction.
Learn more about Nucleophilic substitution from the link given below.
https://brainly.com/question/2017803
#SPJ4
what mass of hydrogen is present in a 200.0 mg sample of water? (hint: calculate percent composition first.)
Mass of hydrogen present in a 200.0 mg sample of water is 22.2g.
The molar weight of water is 18.015 g/mol, and hydrogen has a weight of 1 g/mol.
So mass of hydrogen= (2/18.015)(200)=22.2 grams.
What is hydrogen?
Hydrogen is the first chemical element which is denoted by H. Hydrogen is the lightest element. At trendy conditions hydrogen is a fuel of diatomic molecules having the components H2. it's miles colorless, odorless, tasteless, non-toxic, and enormously flammable.Hydrogen is the maximum ample chemical substance within the universe, constituting kind of 75% of all ordinary dependants.Stars inclusive of the sun are specially composed of hydrogen within the plasma country. most of the hydrogen on this planet exists in molecular bureaucracy including water and organic compounds.To know more about hydrogen, click the link given below:
https://brainly.com/question/19678094
#SPJ4
What type of bond is formaldehyde?
Formaldehyde has a double bond.
Formaldehyde is a molecule that consists of one carbon atom coma one oxygen atom and two hydrogen atoms.
In this atom carbon and oxygen contains two bonds between them. There is one Bond present between each hydrogen atom and the carbon atom. Generally, the double bonds are shorter than the single bond because a single double s weaken than a single bond.
Because of the presence of the double bond between the carbon and oxygen molecule we can say that formaldehyde as a double bond.
To know more about formaldehyde, visit,
brainly.com/question/29550668
#SPJ4
What are the different types of chemical bonds list the 3 types of bonds from strongest to weakest and describe each type of bond?
A chemical bond can be formed by exchange of electrons, sharing of electrons.
There are so many types of chemical bonds but majorly three types of chemical bonds are:
Ionic Bond,
Covalent Bond,
and Metallic Bonds.
And out of these three types of bonds, Ionic Bonds are the strongest bonds.
The order from strongest to weakest bond is given as :
Ionic Bond > Covalent Bond > Metallic Bond
Ionic Bond: When an atom lose or gain the electron to attain the stability it forms ions and the attractive forces between two oppositely charged ions is known as ionic attractions or electrostatic attractive forces.
and such formed bonds are known as ionic bonds.
An ionic bond is formed when the difference between the electronegativities of two atoms is high as an electron transfer to occur to form the ions.
Covalent Bond: A covalent bond consists of the mutual sharing of one or more pairs of electrons between two atoms.
A covalent bond is formed when the electronegativity difference of two atoms is too small for an electron transfer to occur to form ions.
Metallic Bonds: Metallic bonds are made up of electrostatic attraction between metal cations and the delocalized electrons. Metallic bond is collective sharing of valence electrons between several positively charged metal ions.
To know more about Chemical Bonds:
brainly.com/question/15444131
#SPJ4
Which element has the same number of energy levels as krypton (kr) and the same number of valence electrons as nitrogen (n)?.
The element that has the same number of energy levels as Krypton (Kr) and the same number of valence electrons as Nitrogen (n) is Arsenic (As).
What are valence electrons?Electrons аre sub-аtomic pаrticles thаt аre present in the аtom аnd cаrry а negаtive chаrge. The electrons were discovered by J.J. Thompson. The electrons revolve аround the nucleus in vаrious shells аnd аid in the formаtion of bonds.
Vаlence electrons аre the totаl number of electrons thаt аn аtom cаn shаre to form bonds. Nitrogen is the element thаt hаs the sаme number of vаlence electrons аs Arsenic with both of them hаving 5 vаlence electrons.
Krypton is а noble gаs locаted in group VIII А аnd 4rd period. Nitrogen is in the 5fh group. So, we must look for аn element locаted in the 4rd period аnd group VА on the periodic table.
Iron (Fe) ⇒ Iron is in the 4rd period аnd group VIBSelenium (Se) ⇒ Selenium is in the 4rd period аnd group VIААrsenic (Аs) ⇒ Аrsenic is in the 4rd period аnd group VА аnd group VАCаlcium (Cа) ⇒ Cаlcium is locаted in group 4rd аnd group IIАYour question is incomplete, but most probably your full options were
a. selenium (Se)
b. arsenic (As)
c. iron (Fe)
d. calcium (Ca)
Thus, the correct answer is B.
For more information about valence electrons refer to the link:
https://brainly.com/question/28977387
#SPJ4
While attempting to determine the structure of a compound using elemental analysis and functional group tests, you are generally able to recover your original sample.a. Trueb. False
While attempting to determine the structure of a compound using elemental analysis and functional group tests you are generally able to recover your original sample as False.
Neutron activation analysis is a commonly used non-destructive analytical method for determining the identity and concentration of elements in a wide variety of materials. The Sodium Test or La Seigne Test is used in elemental analysis to qualitatively determine the presence of foreign elements such as halogens nitrogen sulfur and phosphorus in organic compounds.
Elemental and chemical state compositions are best determined using low information-depth quantitative techniques such as X-ray photoelectron spectroscopy. The most important spectroscopic techniques for structure elucidation are ultraviolet and visible spectroscopy infrared spectroscopy and nuclear magnetic resonance spectroscopy.
Learn more about Elemental analysis here:- https://brainly.com/question/13408454
#SPJ4
calculate the mass of calcium chloride (cacl2) that is needed to form a 100.0 ml solution of 0.150 m cacl2.
Mass of CaCl2 is 11g .
What is Molar Mass?
We all wish to know how many molecules are there in a given material. Atoms and molecules are very small in both size and mass. One sample mole's weight is the molar mass. To get the molar mass, connect the atomic masses (atomic weights) of each atom in the molecule. Using the mass listed in the Periodic Table or Atomic Weight Table, determine the atomic mass for each element.
Typically, molar mass is stated in either grammes (g) or kilogrammes (kg) (kg).
(100mL) (1L)/1000mL = 0.1 L is the volume of solution in litters.
CaCl2 has a molarity of 1 mole/L and a molar mass of 110 g/mole.
CaCl2 solute mass equals
M = mol of solute per litre of solution; mol of solute equals mol mass of solute divided by molar mass
Mass of the solute is equal to M x L of solution x its molar mass.
CaCl2 mass equals 1 mole/L, 0.1 L, and 110 g/mole, or 11 g CaCl2.
The mass of CaCl2 is equal to 11g CaCl2.
Learn more about Molar Mass from given link
brainly.com/question/837939
#SPJ4
a nuclear fission chain reaction where uranium-235 is bombarded with neutrons produces barium142, krypton-91 and which other type of product?
A nuclear fission chain reaction where uranium-235 is bombarded with neutrons produces barium142, krypton-91 and positrons type of product.
What is Nuclear Fission ?Nuclear fission is a process by which a large nucleus is split into two smaller nuclei, or fission fragments; nuclear fission takes place after the nucleus absorbs a neutron that usually is a product of another atom's radioactive decay.
The newly-formed fission fragments have highly unstable neutron to proton ratios, which makes them extremely radioactive.
What is nuclear fission chain reaction?A chain reaction refers to a process in which neutrons released in fission produce an additional fission in at least one further nucleus. This nucleus in turn produces neutrons, and the process repeats. The process may be controlled (nuclear power) or uncontrolled (nuclear weapons).
In the case of Uranium-235, nuclear fission creates a wide variety of fission fragments, such as
Learn more about nuclear power from brainly.com/question/1010906.
#SPJ4
The united states mint uses electrolysis to copper plate zinc pennies by placing them in a cu2+ solution and connecting the pennies and a copper electrode to a battery. Enter the half-reaction that takes place when the pennies are plated with solid copper. Include phases.
Cathode reaction: [tex]Cu^{2+} + (aq) + 2e-- > Cu (s).\\[/tex]
Anode reaction: [tex]Cu(s) -- > Cu^{2}+ (aq) + 2e[/tex] is
What is half-reaction?
A redox reaction's oxidation or reduction reaction component is known as a half reaction (or half-cell reaction). By taking into account the change in oxidation states of specific chemicals participating in the redox reaction, a half reaction is produced.
Here Zn pennies act as cathode , reduction of [tex]Cu^{2+}[/tex] to Cu take place here.
Cu rod acts as anode,here dissolution of Cu (s) to [tex]Cu^{2+}[/tex] take place .
Half cell reactions
Cathode reaction: [tex]Cu^{2+} + (aq) + 2e-- > Cu (s).\\[/tex]
Anode reaction: [tex]Cu(s) -- > Cu^{2}+ (aq) + 2e[/tex]
To know more about half-reaction checkout https://brainly.com/question/10668307
#SPJ4
Select all the statements that correctly describe the arrangement of individual particles in the three physical states of matter. Relate these particulate views to the observable properties of matter.
Gases occupy the entire volume of the container.
The particles in a solid move quite freely.
The particles in a solid occupy fixed positions.
Liquids take the shape of the container.
Liquids have the same fixed arrangement of particles as observed in solids.
The particles in a gas move quite freely.
The correct statements are statement 1 (Gases occupy the entire volume of the container), statement 3 (The particles in a solid occupy fixed positions), statement 4 (Liquids take the shape of a container), and statement 6 (The particles in a gas move quite freely).
The term "matter" refers to anything that occupies space and has mass. There are three different states of matter: solid, liquid, and gas.
Solids have distinct volumes and shapes. They are not compressible and are densely populated. The particles of a solid are attracted to one another with a powerful force. The distance between solids' particles is minuscule. The particles in a solid are in a fixed location.
A liquid cannot be compressed because it has a fixed volume. They don't have a fixed shape; instead, they take on the shape of the vessel they are placed in.
Gases are compressible. To fill their vessels, gases enlarge. They take up a lot more space than the liquids or solids they originate from.
To know more about states of matter:
https://brainly.com/question/1134312
#SPJ4
Arrange the colors of the visible spectrum in order from highest to lowest energy !
The colors of the visible spectrum are in order from the highest to lowest energy which is : Violet Indigo Blue Green Yellow Orange and Red.
Red light has the lowest energy since it has the longest visible light wavelength. The highest energy visible light is violet since it has the shortest wavelength. The visible light spectrum has energies ranging from red to violet, and the human brain perceives these energy as different hues. Violet has the highest energy whereas red has the lowest. Red light, which has the lowest visible light frequency, has the least energy. The order spectrum reveals frequency content, just like the power spectrum does.
However, the order spectrum offers extra information about harmonically connected rotating machinery systems. Orders are frequency multiples of the reference velocity that are specific.
To learn more about visible spectrum please refer:
brainly.com/question/4901067
#SPJ4
3. A force is a push or a pull. What happens to an object that the magnets attract?
Answer:
it pulls
Explanation:
it pulls because of the magnetic force
Answer: It is pulled
Explanation:
Deeming that the force of motion is attraction, the only way it could be moving would be in pull of the magnet.
Does P and Cl form an ionic bond?
What is bond answer in one sentence?
A chemical bond can be interaction between atoms or ions that enables the formation of molecules and crystals.
A chemical bond can be formed by exchange of electrons, sharing of electrons.
When an atom lose or gain the electron to attain the stability it forms ions and the attractive forces between two oppositely charged ions is known as ionic attractions or electrometric attractive forces.
and such formed bonds are known as ionic bonds.
An ionic bond is formed when the difference between the electronegativities of two atoms is high as an electron transfer to occur to form the ions.
A covalent bond consists of the mutual sharing of one or more pairs of electrons between two atoms.
A covalent bond is formed when the electronegativity difference of two atoms is too small for an electron transfer to occur to form ions.
To know more about Chemical Bonds:
https://brainly.com/question/19382448
#SPJ4
Every second, the Sun converts about 600 million tons of hydrogen into 596 million tons of helium. The remaining 4 million tons of mass is _________.
converted to an amount of energy equal to 4 million tons times the speed of light squared
ejected into space in a solar wind
reabsorbed as molecular hydrogen
ejected into space by solar flares
translated into 4 million tons of energy multiplied by the square of the speed of light.
What percentage of the Sun's mass is converted to energy per second?The Sun undergoes this reaction throughout, and as a result, 600 million tons if hydrogen are converted in 596 million tons or helium each second.E=mc² states that the 4 million tons that missing matter are transformed into energy.
How much of the Sun's hydrogen gets changed into helium every day?The sun makes 598 tons of helium and burns 600 million tons of hydrogen each second.The remaining 4 million tons per day are turned into electricity.
To know more about Sun visit:
https://brainly.com/question/17376727
#SPJ4
explian why potassium chloride, KCI will not dissolve in carbon tetrachloride,CCI4?
What is a homogeneous mixture in which a substance is dissolved in a liquid?
A homogeneous mixture in which a substance is dissolved in a liquid is a solution.
A homogeneous mixture is the that has the same proportion of the components through out the mixture. a homogeneous mixture has the uniform composition through out the mixture. The liquid is called as the solvent which dissolves the other substances is called as the solute. there are some examples of homogeneous mixtures are :
Air sugar waterrain watersalt watervinegarin the homogeneous mixture we can not distinguish the the components of the mixture. so, a solution is a homogeneous mixture in which a substance is dissolved in a liquid.
To learn more about homogeneous mixture here
https://brainly.com/question/3673148
#SPJ4
Given that S is the central atom in OSF4, draw the LewisStructure in which the formal charges of all atoms are zero.Include any lone pair electrons.
In a schematic illustration of a compound called a Lewis structure, the atoms and their associated electrons are shown.
Which Lewis structure for SOF4 has the most lone pairs overall?As a result, each fluorine and oxygen atom contains three lone electron pairs and six non-bonding electrons.
What part of OSF4's structure does the oxygen atom most likely occupy?The equatorial plane The two F atoms would occupy the axial places in accordance with Bent's Rule, and the other two F atoms, along with the oxygen atom, would occupy the equatorial positions. This would result in a triangular bipyramidal structure.
To know more about Lewis Structure visit :-
https://brainly.com/question/29636007
#SPJ4
What are 3 patterns in the periodic table?
Is phosphorus chloride covalent or ionic?
(a) is it possible to grind up and reuse phenol-formaldehyde? why or why not? (b) is it possible to grind up and reuse polypropylene? why or why not?
Phenol-formaldehyde is a thermoset polymer. Thermoset polymers can not be heated up and reused. Therefore it is not possible.
What is Polymer?
The Greek word for "polymer" is "many pieces." Everywhere we look, we encounter polymers. From the strand of human DNA, a biopolymer that naturally occurs, to polypropylene, a material that is used all over the world.
Natural polymers are those found in plants and animals; synthetic polymers are those manufactured by humans (synthetic polymers). Due to their many distinctive physical and chemical characteristics, several polymers are used in daily life.
All polymers are produced by the process of polymerization, in which their component parts, known as monomers, combine with one another to form polymer chains, or 3-dimensional networks that form the links in polymers.
Learn more about Polymer from given link
https://brainly.com/question/766968
#SPJ4
Pressure has little effect on the solubility of liquids and solids because they are almost incompressible. (True or False)
It is true that pressure has little or no impact on the solubility of liquids and solids because they are incompressible.
Pressure is the amount of force applied perpendicularly to an object's surface divided by the surface area across which it is applied. According to Henry's Law, a gas's solubility in a liquid is directly correlated with its pressure above the solution's surface. So the solubility of gas increases with an increase in pressure. The solubility of a solid in a liquid solution is unaffected by pressure changes. This is because liquids barely compress while solids cannot be compressed at all. As a result, pressure has no impact on both.
Therefore, the given statement is true.
To know more about Henry's law:
https://brainly.com/question/3247389
#SPJ4
What is the frequency of an x-ray wave with an energy of 2×10 to the power of -17 jewels in hertz
The frequency of an x-ray wave with an energy of 2×10^(-17) J in hertz is 3.01 × 10^(16) hz.
We can find the value of frequency of an x ray wave by using the relation between energy and frequency.
As we know that,
Energy is directly proportional to the frequency of the wave.
Mathematically,
E = h. f
Where,
E is the energy in joule
f is the frequency of the wave in hertz
h is the planck's constant
Given,
E = 2 × 10^(-17)J
h = 6.63 × 10^(-34) kg.m2/s
By substituting all the values, we get
2 × 10^(-17)J = 6.63 × 10^(-34) kg.m2/s × f
f = 2 × 10^(-17)J / 6.63 × 10^(-34) kg.m2/s
f = 3.01 × 10^(16) hz.
Thus, we concluded that the frequency of an x-ray wave with an energy of 2×10^(-17) J in hertz is 3.01 × 10^(16) hz.
learn more about frequency:
https://brainly.com/question/14419982
#SPJ1
One of the electron transitions in a hydrogen atom produces infrared light with a wavelength of 746. 4 nm. What amount of energy causes this transition?.
The energy of this transition is equal to 4.02 x 10^-19 J.
Calculate the frequency of the light using the equation c = λν, where c is the speed of light (299,792,458 m/s), λ is the wavelength (746.4 nm), and ν is the frequency of the light.
Calculate the energy of the transition using the equation E = hν, where h is Planck's constant (6.626 x 10^-34 J*s) and ν is the frequency of the light.
Calculate the amount of energy caused by the transition by multiplying the energy of the transition by the Avogadro constant (6.022 x 10^23 s^-1).
The amount of energy caused by the transition is 4.02 x 10^-19 J.
For more questions like Energy click the link below:
https://brainly.com/question/16984920
#SPJ4
on a hot summer day, you make a glass of refreshing sweet iced tea by combining boiling water, tea, sugar, and ice. what type of change occurs and how do you know?
A physical change will occur when boiling water, tea, sugar, and ice are combined to form sweet iced tea.
What is a physical change?A physical change is a change affecting the form of a chemical substance, but not its chemical composition.
The characteristics of some physical changes are as follows:
textureshapetemperaturechange in the state of matterAccording to this question, one makes a glass of refreshing sweet iced tea by combining boiling water, tea, sugar, and ice on a hot summer day. The resulting solution is an example of a mixture, which contains constituents that retain their individual identity.
This suggests that the change is a physical change because there is no formation of a new substance.
Learn more about physical change at: https://brainly.com/question/17931044
#SPJ1
You are using a microscope with a 10x eyepiece. What is the approximate focal length of an objective lens which will give a total magnification of 200x? assume a tube length of 160 mm.
The approximate focal length of an objective lens is 8.42 mm.
The magnification of eye piece (m1)=10
Total magnification (m)=200
using,
m=m1*m2
200=10*m2
m2=20
Thus, magnification of objective lens=20
Using the formula for magnification of objective lens,
m2=1+L/f
20=1+0.16/f
f=0.16/19
=0.00842 m
8.42 mm
Therefore, the focal length is 8.42 mm.
To learn more about focal length check the link below:
https://brainly.com/question/9757866
#SPJ4
an unknown hydrocarbon is subjected to elemental analysis. the results of this test show that the compound is 83.24% carbon and 16.76% h. with a molar mass of 72 g/mole, the molecular formula of this compound is:
The empiric molecular formula of this compound when an unknown hydrocarbon is subjected to elemental analysis is C4H9
C = 100.00 - 16.76 = 83.24% if H = 16.76%.
each percentage value by the corresponding atomic mass
H = 16.76/1 = 16.76
C = 83.24/12 = 6.94
Divide by a lesser number.
Remove fraction and multiply by 4 H = 9.64
C = 4 H = 16.76/6.94
= 2.41
C = 6.94/6.94 = 1
Empirical equation: C4H9
Octane, or (C4H9)2 (the hydrocarbon), could be the substance.
By calculating the number of moles of each element from its mass, empirical formulas are generated using empirically measured element masses. Obtaining subscripts for a possible empirical formula by dividing the molar amount of each element by its smallest molar amount.
For more information on empiric formula kindly visit to
https://brainly.com/question/14044066
#SPJ4
indicate the hybridization of the specified atoms. be sure to consider any lone pairs you added to the structure. the structure of cyanazine has 5 atoms highlighted. atom 1 is an n atom bonded to 2 c atoms and 1 h atom through single bonds. atom 2 is an n atom bonded to one c atom through a single bond and one c atom through a double bond. atom 3 is a c atom bonded to one c l atom and one n atom through a single bond and one n atom through a double bond. atom 4 is a c atom that is bonded to three c atoms and one n atom through single bonds. atom 5 is a c atom that is bonded to one c atom through a single bond and one n atom through a triple bond. what is the hybridization of atom 1?
The atom bearing the number 1 has an sp3 hybridization. The hybridization is sp3 because there are four groups surrounding this atom, along with two lone pairs of electrons and two bonds.
How can we quickly tell whether atoms have hybridized?Only the quantity of lone pairs and sigma bonds around an atom are taken into account for determining its hybridization.
The term "hybridization" means what?
When two atomic orbitals join to form a hybrid orbital in a molecule, the energy of the separate atomic orbitals is redistributed to give orbitals of equivalent energy.
To know more about Atom visit:-
brainly.com/question/13654549
#SPJ4
A student is investigating the transfer of thermal energy. The student boils a pot water, removes the pot from the burner, and adds ice cubes to the water. Which direction is the thermal energy flowing in this system?.
The direction of Conduction happens via hotter to colder When materials come into contact, their debris collide.
The strength from the quicker-shifting substance is transferred to the slower-shifting substance till they're shifting on the equal speed. Boiling water on a range is an instance of thermal strength. Thermal strength is produced while the atoms and molecules in a substance vibrate quicker because of a upward thrust in temperature.
Thermal energy actions from warmer frame to chillier frame so we realize that during this test water is a warmer frame while ice cubes are chillier frame so the warmth strength will truely actions from warm frame to the frame.
Read more about the water :
https://brainly.com/question/5060579
#SPJ4