AS/A-Level Chemistry Edexcel- Atomic structure & Periodic Table

Question 1

Orbitals in subshells

Answer 1

• Each takes up a single electron before pairing up

- Pair up with 2 electrons of opposite spin

Question 2

Quatum number formula:

Answer 2

2n^2 n= shell

-Total number of electrons that can occupy any principal shell

Question 3

Arrangement of electrons

Answer 3

Levels- Sublevels- Orbitals

Question 4

Energy in Shells:

Answer 4

Different shells have different amounts of energy. Level 1 contains electrons closest to the nucleus. They have the lowest energy

Question 5

Define Orbital

Answer 5

A region in space where one is likely to find an electron

Question 6

Subshells

Answer 6

Each energy level, split into sub-levels which contain 1 or more orbitals
- order s<p></p>

Question 7

Orbital rules:

Answer 7

1st shell= 1 s orbital
2nd shell= 1 s orbital 2 p orbital
3rd shell= 1 s orbital 3 p orbitals 5 d orbitals
-each orbital can hold to a maximum of 2 electrons

Question 8

Electron configuration order:

Answer 8

1s 2s 2p 3s 3p 4s 3d 4p 4d 4f

Question 9

Pauli’s exclusion principle:

Answer 9

when 2 electrons occupy orbitals, they must spin in opposite directions

Question 10

Filling up of Orbital rules for stability:

Answer 10

Filling the orbitals with the least energy to achieve maximum stability

Question 11

Pauli’s exclusion principal:

Answer 11

No orbital can accommodate more than 2 electrons.

If there are two, they must have an opposite spin

Question 12

Aufbau principal:

Answer 12

Electrons enter the orbital that is available with the lowest energy

Question 13

Hund’s rule:

Answer 13

When there are a number of orbitals of equal energy, electrons first fill them up individually therefore repulsion between electrons is reduced and maximum stability is achieved.

• less repulsion
• lower energy
• more stability

Question 14

Why is chromium’s electronic configuration 3d5 4s1 instead of 4s2 and 3d4?

Answer 14

This is to achieve a more stable arrangement of lower energy, 1 4s electron is promoted to 3d to give unpaired electrons with lower repulsion

Question 15

Odd electronic configuration of elements:

Answer 15

Chromium, Copper, Scandium (d block elements) 4s comes after 3d

Copper-4s is higher than 3d here due to repulsion and to achieve maximum stability. 3d10 4s1

Chromium- 3d5 4s1 instead of 4s2 and 3d4 due to 1 electron being promoted to achieve stability. 3d4 4s2

Scandium- 3d1 4s2 the 4s2 is filled up first but it comes after the 3d orbital in the order.

Potassium- 4s is filled before 3d because 4s has a lower energy level than 3d

Question 16

reminder: shorthand notation

Answer 16

you can abbreviate the first 10 electrons with a noble gas

Question 17

D-block elements:

Answer 17

Transition metals, 4s has higher energy and come after 3d. Sc, Ti, V, Cr, Mn, Fe, Cu, Ni, Zn

Question 18

Reminder: Cations and Anions

Answer 18

Ca2+ (you lose 2 electrons therefore electron is decreased by 2 in the structure as well as atomic no)

S2- (you gain 2 electrons, increased)

Question 19

Periodic table facts:

Answer 19

Number of valence electron= group number (column)

shells/outermost quantum shell number= periods (rows)

Question 20

How to find ions:

Answer 20

In ions, there are more electrons than protons

-less=+ more= -

Question 21

Define first ionisation energy and state the equation:

Answer 21

The energy required to remove an electron from each atom in one mole of atoms in a gaseous state.

X(g) –> X+ (g) + e-

Question 22

Define second ionisation energy and state the equation:

Answer 22

The energy required to remove an electron from each singly charged positive ion in 1 mole of positive ions in a gaseous state

X+(g) –> X2+(g) + e-

Question 23

Define third ionisation energy and state the equation:

Answer 23

The energy required to remove an electron from each doubly charged positive ion in 1 mole of positive ions in a gaseous state

X2+(g) –> X3+(g) + e-

Question 24

What are factors that affect the energy of an electron?

Answer 24

1- The orbital in which the electron exists
2- Nuclear charge of the atom (no. of protons in the nucleus)
3-Repulsion (shielding) experienced by the electron from all the other electrons present

Question 25

What are the factors influencing ionisation energy?

Answer 25

1- Atomic Radii- distance from the centre of the atom to the edge of electron cloud (smaller=higherionisation) 2- Nuclear charge (greater=higher) 3-Shielding

Question 26

Periodicity of Atomic Radii:

Answer 26

- Across a period, radius decreases | - Down a group, radius increases

Question 27

Periodicity: | What happens as your go across a period?

Answer 27

- The number of protons in the nucleus increases. - As this increases, the nuclear charge also increases. - The nucleus is more positive - Shielding does not change

Question 28

Periodicity: | What happens as your go down a group?

Answer 28

- Decrease in first ionisation energy - Number of shells increases - Inner shells of electrons repel the outer-shell of electrons - Electrons are negative and will repel each other, shielding

Question 29

What do larger atomic radii mean?

Answer 29

The larger the atomic radius, the further away the outer electrons are held, the smaller the nuclear attraction of the outer electron will be

Question 30

How does nuclear charge affect the attractive force?

Answer 30

The higher the nuclear charge, the stronger the force of attraction

Question 31

S-block elements:

Answer 31

- Elements in groups 1 and 2 | - S-block element has its highest energy in the S orbital

Question 32

P-block elements:

Answer 32

- Elements in groups 3 to 8 | - Has its highest energy in the P orbital

Question 33

D-block elements:

Answer 33

- Elements scandium to zinc - Yttrium to Calcium in period 5 - No. of electrons in the d-orbitals gradually increases from left to right - D sub0shell is filled

Question 34

Atomic Radii formula:

Answer 34

distance between 2 nuclei and dividing it by 2