C1 Atoms and Elements

All substances made of atoms

An element is made up of 1 type of atom

100 diff elements

Periodic table - rows are periods, columns are groups

Elements in a group have similar properties

Metals are on left, non-metals are right

Staircase dividing line - most elements are metals

Atoms of element shown by chemical symbol eg Oxygen is O

Atom has central nucleus

Nucleus made uo by smaller sub-atomic particles

Sub-atomic particles in nucleus are protons and neutrons

Smaller sub-atomic surround the nucleus --> called electrons

Proton is positively charged --> +1

Neutron is neutral --> 0

Electron is negatively charged --> -1

Number of electrons in atom = number of protons in nucleus

Atoms have no overall electrical charge

Atomic number = number of protons in element

Mass number = protons + neutrons

Mass number is top, atomic number bottom

Enery levels = shells

First energy levels can have 2 electrons

Second, third energy levels can have 8 electrons

In diagram, nucleus shown as black spot

Energy level shown as cricle round nucleus

Electron shown by dot or cross