2-Atoms, elements and compounds

2.1 Elements, compounds and mixture 2.2 Atomic structure and the Periodic Table 2.3 Isotopes

What is an atom?

It’s the building block of an element

What’s an element?

• It’s a substance that cannot be further divided into a simpler substance by chemical methods

• All the atoms of an element contain the same number of proton

How many elements are in the periodic

118 known elements

What are the components of the universe?

Hydrogen 92% and helium all other elements contribute to 1% total

What’s a compound?

A substance formed by the chemical combination of 2 or more elements in fixed proportion

What’s a molecule?

Two or more atoms bonded together chemically. They can be the same element or a different elements.

Examples of molecules?

O2 or H2O

Compounds and molecules FACT

All compounds are molecules, but not all molecules are compounds

What is the difference between compounds and molecules

• Molecules focus on the number of atoms bonded (some are different)

• Compounds focus in different elements bonded together

What is the structure of the atom?

• Nucleus with a proton plus a neutron

• Surrounded by electron shells

What is an electron?

A subatomic particle with a negligible mass and a relative charge of -1

Where are electrons located?

They are present in all atoms and are located in the shells (energy levels) outside the nucleus 

What is a proton

A subatomic particle with a relative atomic mass of 1 and a charge of +1 found in the nucleus of all atoms

What is a neutron

• An uncharged subatomic particle present in the nucleus of atoms

• A neutron has a mass of 1 relative to proton

What is a nucleus

• It’s the central region of an atom that’s made up of the protons and neutrons of the atom

• The electrons orbit around the nucleus in different shells/energy levels

What is a subatomic particle?

Very small particles (proton, neutron, electron) from which all atoms are made from

What is the proton/atomic number

It’s the number of protons in the nucleus of an atom

What’s the atomic/nucleon mass?

The number of protons and neutrons in the nucleons of an atom

What are isotopes?

They are atoms of the same element that have the same proton number but different mass/nucleon number (they have a different number of neutrons in their nuclei)

What is the relative atomic mass?

It’s the weighed average mass of the atoms of an element including all isotopes

How do you know the group number 

It’s the total number of valent electrons in the last shell 

How do you know the period number?

The number of energy shells in electron configuration 

What is electronic configuration/structure?

A shorthand method of describing the arrangement of electrons within electron energy levels of an atom