Topic 2: Atomic Structure

Question 1

Atomic structure

Answer 1

Protons and neutrons (nucleons) are located in the nucleus of the atom.

Electrons are located in energy levels surrounding the nucleus.

Question 2

Relative charges and masses of sub-atomic particle

Answer 2

Sub-atomic particle Relative charge Relative mass

Proton +1 1

Neutron No charge 1

Electron -1 Negligible

Question 3

Principal energy levels

Answer 3

Electrons are located in principal energy levels (these are also known as man energy levels)

Energy levels are assigned names.

The first main energy level is n=1. It has the lowest energy and energy increases as the value of n increases.

Question 4

Which energy level is closest to the nucleus and has the lowest amount of energy.

Answer 4

n=1

Energy increases as the value of n increases

Question 5

How many electrons can each main energy level hold?

Answer 5

Main energy levels can hold a maximum of 2n^2 electrons

e.g - energy level 2

n=2 can hold (2x2^2) = 8 electrons

n=3 can hold (2x3^2) = 18 electrons

Question 6

Sub-levels in the atom

Answer 6

Each main energy level is split into sub-levels

n=1 has 1 sub-level (1s)

n=2 has 2 sub-levels (2s,2p)

n=3 has 3 sub-levels (3s,3p,3d)

n=4 has 4 sub-levels (4s,4p,4d,4f)

Question 7

Within a main energy level, what is the order of sub-levels?

Answer 7

s < p < d < f

s has the lowest energy and f has the highest.

Question 8

How many electrons can each sub-level hold?

Answer 8

s can hold 1 pair of electrons = 2 electrons

p can hold 3 pairs of electrons = 6 electrons

d can hold 5 pairs of electrons = 10 electrons

f can hold 7 pairs of electrons = 14 electrons

Question 9

Atomic number (Z)

Answer 9

The atomic number is the number of protons in the nucleus of an atom.

Question 10

The mass number (A)

Answer 10

The mass number is the total number of protons and neutrons in the nucleus of an atom.

Question 11

How can you determine the number of neutrons in an atom?

Answer 11

Subtract the atomic number from the mass number.

Question 12

Ions

Answer 12

Ions are atoms of elements that have lost or gained electrons.

There are two types of ions.

Positively charged cations and negatively charged anions.

Question 13

What is an isotope?

What are the three naturally occurring isotopes of carbon?

Answer 13

Isotopes are atoms that have the same atomic number but a different mass number. This means that they have the same number of protons but a different number of neutrons.

The three naturally occurring isotopes of carbon are:
- carbon 12
- carbon 13
- carbon 14

Question 14

Properties of isotopes

Answer 14

Isotopes of an element have different physical properties to eachother, but identical chemical properties.

Heavier isotopes have higher melting/boiling points and higher densities.

Question 15

Relative abundance of isotopes

Answer 15

The relative abundance of an isotope is the percentage of atoms with a specific mass number in a naturally occurring sample of the element.

Question 16

What is a mass spectrum?

Answer 16

A mass spectrum is produced by a mass spectrometer. A mass spectrum shows mass : charge ratio on the x axis, and relative abundance on the y axis.

Question 17

How to calculate the RAM

Answer 17

Multiply the mass number of each isotope by its relative abundance. We add each of these together and divide by 100.

RAM = (Mass number x Relative abundance) / 100

RAM is dimensionless, meaning it does not have a unit.

Question 18

e.g question - RAM

Bromine (Ar = 79.80) has two isotopes, 79Br and 81Br. Calculate the relative abundance of each isotope.

Answer 18

To solve this, we set up the equation like this.

79.90 = 81(x) + 79(100-x)
————————
100

We then solve this for x.

Question 19

Atomic orbitals

Answer 19

Atomic orbitals represent a region of space where there is a high probability of finding an electron.

Question 20

S orbitals

Answer 20

S orbitals are spherical. Each s orbital can hold a maximum of 2 electrons with opposite spins, according to the Pauli exclusion principle.

Question 21

P orbitals

Answer 21

P orbitals are ‘dumbbell’ shaped.

Within the p sub-level, there are 3 p orbitals. px, py, pz.

The x, y, and z, refer to the orientation of the orbital.

Each p orbital can hold a maximum of 2 electron with opposite spins. The p sub level holds a total of 6 electrons.

Question 22

The aufbau principle.

Answer 22

The aufbau principle is used to determine the electron configuration of an atom or ion.

According to the principle, electrons fill lowest energy orbitals first. The lowest energy is the 1s orbital. As we go up, the energy of the orbital increases.

Question 23

Pauli exclusion principle

Answer 23

An atomic orbital can hold a maximum of 2 electrons with opposite spins

Question 24

Hund’s rule

Answer 24

Degenerate orbitals in a sub-level (e.g px,py,pz) are singly occupied by electrons before being doubly occupied. The electrons have the same spin.

Question 25

Which sub-levels do ions lose electrons from?

Answer 25

Ions lose electrons from the highest-energy sub-level first.

For example, sodium ions lose their electron from the 3s sub-level (as it is the sub-level with the highest energy).

Question 26

Electron configuration exceptions: chromium and copper

Answer 26

There are two exceptions to the Aufbau principle. The electron configurations of chromium and copper don’t follow the rule.

Instead of chromium having ‘3d4, 4s2’ it has ‘3d5, 4s1’.

Instead of copper having ‘3d9, 4s2’ it has ‘3d10, 4s1’.

The reason for this, is that a half full or full d sub-level is more stable than a partially filled d-sub level and so an electron from the 4s orbital is excited and rises to the 3d orbital.

Question 27

Electromagnetic spectrum

Answer 27

An electromagnetic spectrum shows all the frequencies of electromagnetic radiation.

Question 28

Frequencies on the electromagnetic spectrum (right—>left) (increasing energy)

Answer 28

Radio waves

Microwaves

Infrared radiation

Visible light

Ultraviolet

X-rays

Gamma rays

Question 29

What is the relationship between wavelength and frequency?

Answer 29

Waves with high frequency have shorter wavelengths.

Waves with lower frequencies have longer wavelengths.

Question 30

Wavelength

Answer 30

The distance between two crests of a wave

Question 31

What is the equation involving speed, wavelength, and frequency?

What are the units?

Answer 31

c = λ x v
speed = wavelength x frequency

Units:
c m s⁻¹
λ m
s s⁻¹

Question 32

Within the visible light spectrum, which colour has the highest energy and which has the lowest?

Which colour has the shortest wavelength? Which has the longest?

Answer 32

Red light has the lowest energy. It is found on the right side of the VL spectrum.
Violet light has the highest energy. It is found on the left side of the VL spectrum.

Violet has the shortest wavelength (as it has the highest energy)
Red has the longest wavelength (as it has the least energy)

Question 33

Continuous spectrum

Answer 33

A continuous spectrum shows all wavelengths of visible light from red to violet.

If you pass white light through a prism, dispersion occurs, and the white light splits up into all the wavelengths of visible light from red to violet.

Question 34

Absorption line spectrum

Answer 34

Has black lines on a coloured background. Certain wavelengths of visible light are missing from the absorption line spectrum.

Question 35

Emission line spectrum

Answer 35

Consists of coloured lines on a black background. Only certain wavelengths of visible light can be seen.

Question 36

Spectroscope

Answer 36

A spectroscope is used to split the light into its different wavelengths

Question 37

Colours of light visible in the electromagnetic spectrum

Answer 37

R ed
O orange
Y ellow
G reen
B lue
I ndigo
V iolet

Question 38

What are the wavelengths present in the visible region of the electromagnetic spectrum

Answer 38

400-700nm

Question 39

Where do the lines on a line spectra converge?

Answer 39

Lines converge at higher energies. This is because the energy levels inside the atoms are closer together at higher energies.

Question 40

What happens when an atom absorbs energy?

Answer 40

Electrons are promoted to higher energy levels when they absorb energy. This is known as the excited state, however it is unstable and the electron soon falls back to the lowest level or ground state. When the electron falls, it emits a photon. The energy of this photon is proportional to change in energy of the atom.

Question 41

What series is produced when an excited electron falls to n=1?

Answer 41

Lyman series

Ultraviolet radiation is produced.

Question 42

What series is produced when an excited electron falls to n=2?

Answer 42

Balmer series

Visible light radiation is produced.

Question 43

What series is produced when an excited electron falls to n=3?

Answer 43

Paschen series

Infrared radiation is produced.

Question 44

Flame tests

What happens during a flame test?

Answer 44

A flame test is a qualitative test that can be used to identify metal ions in a solution.

In a flame test, a sample containing a solution of metal ions is heated in a flame. The different metal ions produce different colours when heated.

When the metal ion atom is heated, it absorbs energy and electrons are promoted to excited states. When they fall to their ground state, the atom emits a photon. The wavelength of the photon emitted corresponds to a colour. That is the colour that is produced during the flame test.