AtomsAtoms are the building blocks for the whole Universe.

Matter is composed of elements, which are made from small particles called atoms.

Physical substances are composed of matter.

Atoms are the smallest distinguishable part of an element. Every element, such as hydrogen, carbon or gold, is composed of just one type of atom.

Next >

AtomsAtoms are NOT solid spheres of matter as was once thought.

Although atoms are the smallest distinguishable unit of an element, they are made up of three different sub-atomic particles:

•Protons

ElectronNeutronProton

Carbon atom (C)

Next >

•Neutrons

•Electrons

1

What is the name given to the smallest distinguishable unit of an element?

Question

A) Atom

B) Molecule

C) Particle

D) Matter

AtomsProtons and neutrons are found in the middle of the atom, the nucleus. They cluster together forming nucleons. Electrons are much smaller than the nucleons, and orbit (rapidly move around) the nucleus at a considerable distance from it.

For example, if an atom was a soccer field, then the nucleus would be about the size of a soccer ball in the center of the field.

Next >

The rest of the atom is empty space.

ElectronNucleus (consisting of protons

and neutrons)

Carbon atom (C)

2

Which of the following is NOT found in the nucleus of any atom?

Question

A) Proton

B) Neutron

C) Nucleon

D) Electron

Particle Charges

Particle Name

Relative Mass

Relative Charge

Proton 1 1

Neutron 1 0

Electron 1/1836 -1

Protons, neutrons and electrons have different relative electrical charges and masses.

Nearly all the mass of an atom is in the positively charged nucleus.

The mass of electrons is negligible compared with that of the protons and neutrons.

It is the attractions between the positively charged nucleus and the negative charged electrons that holds the electrons orbiting (moving) around the nucleus.

Next >

Atomic NumberThe number of protons in an atom is very important because all atoms of the same element have the same number of protons.

For example, the simplest atom, hydrogen (H) always has one proton and an atom of carbon (C) always has six protons.

The atomic number is equal to the number of protons in an atom's nucleus. The atomic number determines which element an atom is.

One electronDirection of

electronorbit

One proton in the nucleus

Hydrogen atom (H)

Next >

Mass Number

Next >

Electrons are not counted, as they are so light compared to the nucleons that they make very little difference to the overall mass.

The number of neutrons within an atom can therefore be found by subtracting the atomic number from the mass number.

The mass of an atom is the total number of protons and neutrons (nucleons) it contains.

Magnesium (Mg)

12 protons and12 neutrons,

8 protons and8 neutrons,

Atomic Mass number = 24

Mass number = 16

Oxygen (O)

Carbon-12Mass number = 12stable

Carbon-13Mass number = 13

stable

Carbon-14Mass number = 14unstable(radioactive)

Isotopes

•Atoms of the same element with different numbers of neutrons, and therefore different atomic masses, are called isotopes.

Many of the most common and important elements have several naturally occurring isotopes.

Carbon (C), which is found in all living things, has three isotopes: carbon-12, carbon-13 and carbon-14.

Next >

Atoms of an element always have the same number of protons, but may have different numbers of neutrons.

Relative Atomic MassBy finding out the proportions of all the isotopes for an element, it is possible to find an average, known as the relative atomic mass (Ar).

The chemical symbol, atomic number and relative atomic mass of any element can be found on a special chart known as ‘The Periodic Table’.

This is the mean weight for an atom of any given element.

Each cell on the table shows important information about an element.

Element

2

HeHelium

4.003

Atomic Number

Symbol

NameRelativeAtomic Mass (Ar)

Helium

Next >

Electron Structure

All chemical reactions are based around changes to the number and location of the electrons orbiting the nucleus.

All single atoms of elements have the same number of protons (charge +1) as electrons (charge -1), so their net charge is zero.

ElectronProton Neutron

Neon (Ne) atom

Next >

The electronic structure, number and arrangement of electrons within an atom, determines the properties of an atom.

3

''Isotopes are atoms of the same element containing the same number of protons and electrons but different numbers of neutrons.'' Is this statement true or false?

Answer True or False.

Question

Electron Structure

Each electron in an atom is in a particular energy level (or shell) and the electrons must occupy the lowest available energy level (or shell) available nearest the nucleus.

Electrons move rapidly around the nucleus (orbit) in distinct energy levels (shells).

When a shell is full the next electron goes into the next lowest available energy level.

Next >

Nickel (Ni) atom

Energylevels (shells)

Increasing energy of energy levels

Electron Structure

Next >

1st shell = 2 electrons

2nd shell =8 electrons

Each energy level is capable of holding only a certain number of electrons.

The first energy level can hold only two electrons. This energy level is filled first.

The second energy level can hold eight electrons. This energy level is filled after the first energy level is complete (full).

There are further energy levels, each containing larger numbers of electrons. We will refer to these as outer shells.

Outer shells

4

Electrons move rapidly around the nucleus in distinct orbits (energy levels). The second energy level can hold a maximum of....

Question

A) one electron.

B) ten electrons.

C) eight electrons.

D) eighteen electrons.