chem exam revision

Question 1

What is the Atomic number?

Answer 1

The number of protons in the nucleus of an atom; identical to the charge number of the nucleus

Question 2

What is the mass number?

Answer 2

The number of protons and neutrons in the nucleus of an atom

Question 3

What are isotopes?

Answer 3

isotopes have the same number of protons but different number of neutrons EG: 12C and 13C are isotopes of carbon.

Question 4

What is the Bohr model?

Answer 4

A theory which states that electrons in an atom occupy fixed, circular orbits that correspond to specific energy levels.

Question 5

What is the Schrodinger model?

Answer 5

A model for the behaiour of electrons in atoms. It describes electrons as having wave-like properties.

Question 6

What is subshell configuration?

Answer 6

Electron Configuration describes how the electrons are distributed in an atom’s orbitals. The electrons are arranged in four subshells namely s,p, d and f. The electron configuration of each atom is represented by following a standard notation.

For example, the electron configuration of Sodium is 1s22s22p63s1.

Question 7

Describe the trend of effective nuclear charge in the periodic table

Answer 7

Increases from left to right across a period (The valence electrons are more attracted toe nucleus as the effective nuclear charge increases)
Remains constant down a group (Valence electrons held less strongly as they are further from the nucleus because there are more shells in the atom)

Question 8

Describe the trend of electronegativity in the periodic table

Answer 8

Decreases down a group (The valence electrons are less strongly attracted to the nucleus as they are further from the nucleus)
Increases left to right across a period (The valence electrons become more strongly attraced to the nucleus as the core charge increases).

Question 9

Describe the trend of atomic radius in the periodic table

Answer 9

Increases down a group (The number of shells increases)
Decreases left to right across a period (Core charge increases)

Question 10

Describe the trend of first ionisation energy in the periodic table

Answer 10

Decreases down a group (The valence electrons are less attracted to the nucleus as they are further from the nucleus)
Increases left to right across a group (The core charge increases)

Question 11

What are Lewis Structures?

Answer 11

It is used to show how the electrons are arranged around individual atoms in a molecule. Electrons are shown as “dots” or for bonding electrons as a line between the two atoms.

Question 12

What is the VSEPR theory?

Answer 12

Valence Shell Electron Pair Repulsion Theory
A model used to predict the shape of molecules. The basis of VSEPR is that the valence electron pairs surrounding an atom mutually repel each other, and therefore adopt an arrangement that minimises this repulsion, thus determining the molecular shape.
4 - tetrahedral 3 - pyramidal 2 - bent 1 - linear

Question 13

What is electronegativity and polar bonds?

Answer 13

Electronegativity is the abiliy of an atom to attract electrons move from a metal atom to a non-metal to form ions. Polar bonds are bonds or molecules with a permanent dipole (separation into positive and negative charges). They have an uneven distribution of charge.

Question 14

Describe the polarity of polyatomic molecules

Answer 14

Polarity of polyatomic molecules depends on the shape of the molecule, as well as the polarity of its covalent bonds. A molecule can possess polar bonds yet still be non-polar. Molecules that contain only non-polar bonds are non-polar molecules.

Question 15

What are symmetrical and asymmetrical molecules?

Answer 15

Polyatomic molecules are split into symmetrical molecules (molecules that contain polar bonds that are evenly distributed are non-polar, as the bond dipoles cancel each other out) and asymmetrical molecules (contain polar bonds are polar molecules, as a net dipole is created in the molecule).

Question 16

What are intermolecular forces?

Answer 16

An electrostatic force of attraction between molecule, including dipole-dipole forces, hydrogen bonds and dispersion forces.

Question 17

What are dispersion forces?

Answer 17

The force of attraction between molecules due to temporary dipoles induced in the molecules. The temporary dipoles are the result of random fluctuation in the electron density

Question 18

What is dipole-dipole attraction?

Answer 18

A form of intermolecular forces that occurs between polar molecules where the partially positively charged end of one molecule is attracted to the partially negatively charged end of another molecule.

Question 19

What is hydrogen bonding?

Answer 19

A type of intermolecular, dipole-dipole force where a hydrogen atom is covalently bonded to a highly electronegative atom such as oxygen, nitrogen or fluorine. Due to the disparity of electronegativity values between the atoms involved, the hydrogen devlops a partial positive charge and bonds to lone pairs of electrons on neighbouring atoms of oxygen, nitrogen or fluorine.

Question 20

What is molecular size and intermolecular forces

Answer 20

Dispersion forces occur between all molecules; those that are polar as well as those that are non-polar. In substances with large molecular masses, the dispersion forces between molecules can even be stronger than dipole-dipole attraction and hydrogen bonding.

Question 21

What are the intramolecular forces?

Answer 21

A force that holds the atoms within a molecule together.

Question 22

State the 9 general properties of metals

Answer 22

1. have relatively high melting points and boiling points
2. good conductors of electricity
3. good conductors of heat
4. malleable
5. ductile
6. lustruous
7. often hard, with igh tensile strength
8. have low ionisation energies and electronegativities
9. generally have high densities

Question 23

What is the metallic bonding model?

Answer 23

Positive metal ions are surrounded by a sea of delocalised electrons

Question 24

What is the reactivity of metals in the periodic table?

Answer 24

Metal reactivity decreases across the period. Metal reactivity increases down the group.

Question 25

What is the linear and circular economy?

Answer 25

A linear economy is where products become waste. A circular economy is where products are recycled to make new products. By recycling metals such as aluminium, the aluminium can be used to make new aluminium cans.

Question 26

What is the linear and circular economy?

Answer 26

A linear economy is where products become waste. A circular economy is where products are recycled to make new products. By recycling metals such as aluminium, the aluminium can be used to make new aluminium cans.

Question 27

What are the 5 properties of ionic compounds?

Answer 27

1. have high melting and boiling points
2. are hard but brittle
3. do not conduct electricity in the solid state
4. are good conductors of electricity in the liquid state or when dissolved in water
5. vary from very soluble to insoluble in water

Question 28

What is the ionic bonding model?

Answer 28

A three-dimensional lattice of cations and anions