CHem chapter 1

Elements and the periodic table

the definitions of elements, isotopes and ions, including appropriate notation: atomic number; mass

number; and number of protons, neutrons and electrons

the periodic table as an organisational tool to identify patterns and trends in, and relationships

between, the structures (including shell and subshell electronic configurations and atomic radii) and

properties (including electronegativity, first ionisation energy, metallic and non-metallic character

and reactivity) of elements

critical elements (for example, helium, phosphorus, rare-earth elements and post-transition metals

and metalloids) and the importance of recycling processes for element recovery

CHAPTER 1A – Atoms and elements

In 1802, an English scientist called John Dalton presented the first atomic theory

of matter.

Elements: Materials containing just one type of atom 🡪 Can’t be broken down

into simpler substances

Compounds: Materials containing different types of atoms in simple whole

number ratios

Molecules: Substances that consist of 2 or more atoms that are chemically

combined 🡪 atoms can be the same or different

Matter is made up of

tiny spherical particles

(atoms), which are

indivisible and

indestructible.

Atoms are divided

into subatomic

particles

Diatomic

molecule

Elements & Compounds

Most non-metallic elements form molecules with a definite number of atoms.

Eg. Sulfur (S8)

Some non-metals form covalent network lattices or giant molecules.

Eg. Carbon as graphite or diamond

Several non-metallic elements are

monatomic: exist as individual atoms

Monatomic elements are known as noble gases

Eg. Helium, neon, argon 🡪 Chemically inert = unreactive

What is a lattice?

It is a regularly repeated

3D arrangement atoms.

Elements & Compounds

The atoms in compounds can also form molecules or large networks of atoms.

Atoms

All matter is made up of atoms.

Model: Description that scientists use to represent important features of what they are

trying to describe.

Rutherford’s nuclear model

- Describes atom being mostly empty space, with a central structure known as the nucleus

- Nucleus contains most mass of the atom

- Nucleus is made up of protons & neutrons

- Empty space around nucleus sits the electron cloud, containing

electrons that orbits the nucleus

Subatomic particles: Protons, neutrons & electrons.

Refresher Quiz: How much do you remember from Year 10?

What charge do protons, neutrons & electrons have?

What is the very centre of an atom called?

Which particle (protons, neutrons or electrons) is involved in

reactivity (allows atoms to react with one another)?

Electrons, Protons & Neutrons

Around 99.97% of

atom’s mass

Protons & neutrons

are collectively

known as nucleons

Electrostatic

Attraction: -ve

particles attract to

+ve particles

Why don’t electrons stay

away from the nucleus?

Electrons, Protons & Neutrons

Nucleus of atom is ~ 10,000 - 100,000 times smaller than the size of the atom.

It is like a pea or marble

in the MCG.

Quick Questions

Which subatomic particle corresponds to the following charges:

- Positive

- Neutral

- Negative

Which particle is the smallest in size? Which has the lightest mass?

Which ones are similar in mass?

Smallest in size = Electrons

Lightest in mass = Electrons

Similar in mass = Protons & Neutrons

Isotopes

All atoms that belong to the same element have the same number of protons in the nucleus and therefore

the same atomic number, Z. However, not all atoms that belong to the same element have the same mass

number, A.

Isotopes: Atoms that have the same number of protons (atomic number) but different numbers of neutrons

(and therefore different mass numbers)

Isotopes have similar chemical properties because the electrons that partake in the reactions aren’t affected.

However, isotopes have different physical properties due to their different masses.

Quick Question

Write the isotopic symbol or notation for these 3 naturally occurring carbon

isotopes.

CHAPTER 1B and 1C – The periodic table

Atomic Number (Z): Number of protons in the nucleus of an atom of an element.

- also corresponds to number of electrons in a neutrally charged atom 🡪 equal positive

& negative charge

Mass Number (A): Number of protons & neutrons added together.

Elements are usually represented as the following isotopic symbol/notation:

Iron has 26

protons

& 26 electrons.

Quick Maths:

A-Z = no. of

neutrons

Chemical symbol

of iron

Quiz Question

Determine Z, A, the number of electrons and the number of neutrons for the

following elements:

Z = 29

A = 63

Number of electrons = 29

Number of neutrons = A – Z = 63 – 29 = 34

Z = 36

A = 78

Number of electrons = 36

Number of neutrons = A – Z = 78 – 36 = 42

Z = 2

A = 4

Number of electrons = 2

Number of neutrons = A – Z = 4 – 2 = 2

Trends in the periodic table

Electronegativity - YouTube

How did scientists find out the arrangement of

electrons for other atoms?

- Study of successive ionisation energies in different

elements

Ionisation energy: Energy required to remove an

electron from an atom

Electron that is least strongly attracted to the nucleus

will be removed most easily.

Electrons in same shell:

- are about the same distance from nucleus

- have about the same energy

Schrodinger Model

Also known as quantum mechanical model

Quantum = A specific amount (of energy)

Erwin Schrodinger proposed that electrons behaved as waves around the

nucleus

Currently used today

Difference between this model & the Bohr model:

The way they view electrons

- Bohr 🡪 electrons are tiny, hard particles that revolve around the

nucleus in circular orbits

- Schrodinger 🡪 electrons have wave-like properties

The electron energy levels

- Bohr 🡪 proposed that all electrons in the one shell were of equal

energy

- Schrodinger 🡪 proposed that there were different electronic

energy levels called subshells within a shell

Electronic Configuration – Bohr Shell Model

Electronic Configuration: Arrangement of electrons in shells around the nucleus

1. Electrons generally occupy inner shells (closest to nucleus) before outer shells.

2. Maximum number of electrons in each shell = 2n2 🡪 n is shell number/energy level

3. Electrons fill in a particular order 🡪 From Potassium (Z=19) onwards

- 3rd shell fills to 8, then 4th shell fills to 2, followed by the rest of the e- filling the 3rd shell

till 18. The 4th shell will fill up till 32 once the 3rd shell is full.

eg. Titanium (Z = 22) 🡪 2,8,10,2

Let’s Practice

Determine the electronic configuration for Selenium & draw its Bohr diagram.

How many valence electrons are present in an atom of sulfur?

Look for selenium in the periodic table. Find Z.

Z = 34

2. Apply the rules.

Answer: 2, 8, 18, 6

1. Look for sulfur in the periodic table. Find Z.

Z = 16

2. Apply the rules.

2 in the first shell, 8 in the second shell & 6 in the third shell.

3. The valence electrons = electrons on the outermost shell.

Answer: There are 6 electrons on the outermost shell.

Valence Electrons

The outermost shell of an atom is known as its

valance shell.

The electrons in this shell are known as valance

electrons.

To remove the valance electrons not much energy is required.

These are the electrons involved in reactions.

In order to achieve stability the atom will aim to have 8

electrons in the outermost shell (octet rule).

Limitations of the Shell Model

The shell model doesn’t explain the various differences in energies between

the electron shells.

It also implied that electrons orbit the nucleus in exactly circular paths.

The model can’t accurately predict the emission spectra of atoms with >1

electrons.

It is unable to explain why electron shells can only hold 2n2 electrons

The order of electrons filling of the shells is not explained by this model either

Schrodinger Model

Shells: Major energy levels in an atom

Total no. of e-s per shell = 2n2

These shells contain separate energy levels of

similar energy called subshells 🡪 s, p, d & f

Each subshell can only hold a certain number of

electrons

Within each subshell, electrons occupy a 3D

space around the nucleus known as the orbital

An orbital may be visualised as a blurry cloud of

negative charge

The cloud is most

dense where the

probability of

finding the e- is

large, and vice

versa.

The Pauli Exclusion and Aufbau Principle

One of the key rules about orbitals is

the Pauli exclusion principle which

states that the maximum number of

electrons in an orbital is 2. Therefore,

it could hold 0, 1 or 2 electrons.

The Aufbau principle states that

electrons fill the lowest energy shells

or energy levels first.

Schrodinger Model

What does the fourth shell

contain? ☺

Electronic Configuration

Schrödinger Model

Each dashed line represents

an orbital (each orbital

holds 2 electrons)

This shows the

order in which

subshells are

filled .

The 4s orbital

has a lower

energy state

(why it is filled

first).

Schrodinger Model

This model is able to do what the Bohr model couldn’t 🡪 predict the maximum

number of electrons that each shell can hold

Order of subshell filling = 1s<2s<2p<3s<3p<4s<3d<4p (<5s<4d<5p<6s…)

Schrodinger electronic configuration specifies subshells that electrons occupy

eg. Sodium (Z= 11) 🡪 11 e-s

In shell 1 🡪 2 e-s in s-subshell

In shell 2 🡪 2 e-s in s-subshell

6 e-s in p-subshell

In shell 3 🡪 1 e- in s-subshell

Rules:

1. Lowest orbitals filled first.

2. Each orbital contains a max of 2 electrons

3. Follow the order of filling

Schrodinger Model

THERE ARE SPECIAL EXCEPTIONS:

For chromium (Z=24) & copper (Z=29)

Scientists determined that as a subshell fills, a single electron is

placed in each orbital first. Then, a second electron is entered into the orbitals until

the filling process is complete.

For Chromium, the 3d54s1 configuration is more stable than 3d44s2 configuration

because each of the 5 d-orbitals is exactly half filled.

For Copper, the 3d104s1 arrangement with 5 completely filled orbitals is more stable

than 3d94s2 configuration with partially filled orbitals.

Let’s Practice!

Write the Schrodinger model of electronic configuration for a Vanadium atom

with 23 atoms.

1. Recall the order in which subshells fill & number of orbitals by listing them

down.

2. Fill the subshells by assigning 2 e-s per orbital.

1s 🡪 2 e-s

2s 🡪 2 e-s

2p 🡪 6 e-s

3s 🡪 2 e-s

3p 🡪 6 e-s

4s 🡪 2 e-s

3d 🡪 3 e-s

3. Write the electronic configuration.

1s22s22p63s23p64s23d3

Note that once the order of filling

has been determined, the

subshells are written in

increasing numerical order, not

the order of increasing energy!

Try these yourself!

Write the the Schrodinger model of electronic configuration for:

Lithium

Magnesium

Potassium

Nickel

Excited States

When an atom moves to a higher energy level when excited 🡪 electron

configuration changes

Outermost electron moves to higher energy level subshell

Eg. Sodium

1s22s22p63s1 🡪 1s22s22p63p1

The group and period in which an element is found is easily read from the

electronic configuration

Let’s Practice!

An element X has configuration 1s22s22p63s23p4.

(a) What group is it in?

(b) What period is it in?

(c) Give its name & symbol.

(a) Group 🡪 no. of valence electrons = 6

(b) Period 🡪 highest shell number being filled = 3

(c) Name = Sulfur, Symbol = S

Try to do this question!

Using a fluorine atom as an example, explain the difference between the terms

‘shell’, ‘subshell’ and ‘orbital’.

Answer:

A fluorine atom has 9 electrons. Electrons are arranged in energy levels called

shells; 2 electrons in the first shell and 7 electrons in the second shell, which

could be written as 2, 7.

Shells are made of energy levels called subshells. The first shell has an s-type

subshell; 1s. The second shell has both s- and p- type subshells; 2s and 2p

respectively.

Within subshells, electrons occupy regions of space knows as orbitals. Each

orbital can hold 2 electrons. Subshells of an s-type contain 1 orbital and p-type

subshells contain 3 orbitals. The electronic arrangement in the subshells of a

fluorine atom is 1s22s22p5

CHAPTER 1D – Recycling critical elements

Elements that are in limited supply unless they are recycled as sources could become depleted in

50-100 years are considered critical elements.

The supply, demand and discovery of new reserves of these elements are constantly changing.

Important for industry and technology development.

What Are Rare Earth Elements? - YouTube

Some Transition Metals Uses

Palladium (Pd-46): jewellry, watch making, aircraft spark plugs, surgical instruments

Osium (Os- 76): an alloy to produce fountain pen tips, needles

Iridium (Ir – 77): Found in the Earth’s crust, used in making satellites

Platinum (Pt – 78): Computer hard disks

Recycling

As both population and

dependency on materials continue

to increase, the rate at which

Earth’s reserves are being used is

not sustainable.