Chapter 1. Atomic Structure

Question 1

Name the three sub-atomic particles.

Answer 1

Protons, electrons and neutrons

Question 2

What are nucleons?

Answer 2

Contents of the nucleus of an atom: protons and neutrons

Question 3

Describe the deflection of particles when a beam of electrons, protons and neutrons enters an electric field

Answer 3

Electrons are deflected towards the positive side, protons towards the negative side and neutrons are not deflected. Electrons are deflected more because they have a smaller mass than protons.

Question 4

What is the strong nuclear force and the electrostatic force?

Answer 4

The nuclear force is the force that holds together the protons and neutrons in the nucleus and overcomes the repulsion of the protons and the electrostatic force is the force that holds the electrons and protons together in the atom. The nuclear force is stronger than the electrostatic force.

Question 5

What is the atomic number or the proton number Z?

Answer 5

The number of protons in the nucleus of an atom

Question 6

What determines the chemical properties of an atom?

Answer 6

The number of electrons in the outermost shell of the atom.

Question 7

What is the mass number or the nucleon number A?

Answer 7

The number of protons and neutrons in an atom.

Question 8

What is the atomic radius?

Answer 8

It is half the distance between the two centers of a pair of electrons

Question 9

Describe the periodicity of atomic radius

Answer 9

It decreases across each period, and it increases down a group.

Question 10

Explain why atomic radii decreases across a period

Answer 10

As we move across a period, the charge on a nucleus increases which increases the force of attraction between the nucleus and the electrons in the outer shell.

Question 11

What are isotopes

Answer 11

Atoms of the same element with the same proton number but different number of neutrons

Question 12

Why do isotopes have the same chemical properties

Answer 12

Because they have the same number of electrons in the outer shell

Question 13

What are the three general rules for electronic configuration. Explain

Answer 13

1. Aufbau principle - in the ground state of an atom, the electrons must occupy the orbitals in the order of increasing energy i.e 1s 2s 2p 3s 3p 4s 3d 4p etc
2. Pauli’s exclusion principle- an orbital can only accommodate a maximum of two electrons which must have opposite spins
3. Hund’s rule - in a set of degenerate orbitals , electrons must occupy the orbitals singly first before pairing

Question 14

Explain what is meant by degenerate orbitals

Answer 14

These are orbitals at the same energy level

Question 15

What is the first ionisation energy

Answer 15

The energy needed to remove one electron from each atom in one mole of atoms of an element in the gaseous state
H_(g) ==> H⁺_(g) + e^-

Question 16

What are the trends of ionization energies of elements on a periodic table and explain how

Answer 16

1. Across a period they generally increase since nuclear charge increases which makes it harder to remove electrons but there are two sudden drops due to electrons being removed from a spin pair among single filled sub shells or the removal of an electron from a p orbital which gets shielding from an s orbital
2. Down a group ionization energy decreases as atomic radius increases. Shielding also increases.

Question 17

What is the formula for the max number of electrons that can occupy a principal quantum number

Answer 17

2n²

Question 18

What are the factors that affect the ionisation energy of elements

Answer 18

1.Nuclear attraction
-Ionisation energy increases as proton number increases
2.Distance from the electrons to the nucleus
-ionisation energy decreases when the distance of electrons from the nucleus increases. Larger atoms have weaker forces of attraction
3.Shielding effect
-ionisation energy decreases as shielding effect increases
4.Nuclear charge

Question 19

Explain the periodicity of ionic radii.

Answer 19

Positive ions are smaller than their parent atoms because they would have lost electrons and the opposite is true for negative ions. As we go accross a period the positive ions get smaller as nuclear charge increases then there’s a jump in size when negative ions start to form where the extra electrons in the outer shell cause extra repulsion and they continue to decrease in size because of the increase in nuclear charge.

Question 20

What is the meaning of isotonic?

Answer 20

Same number of neutrons

Question 21

What is the meaning of isotopic?

Answer 21

Same number of protons

Question 22

Note

Answer 22

For a charged particle the proton number does not change but the number of electrons is the one that changes.

Question 23

Give the orbitals that are in our syllabus

Answer 23

s, p_x, p_y, p_z, d_xy, d_yz, d_xz, d_x²-y², dz²