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<aside> 💡 KEY TERMS - for revision

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the structure of atoms

atom → the smallest particle of an element

• can be divided into smaller particles called subatomic particles

atoms are made up of subatomic particles → proton, neutron and electron

• an atom contains a nucleus, which is made up of protons and neutrons
• around the nucleus → electrons
  • smaller than protons and neutrons.

mass of a proton → 1

mass of neutron → 1

mass of electron → 1/1840

• mass of an atom is concentrated on nucleus

charge of subatomic particles:

• proton → positive
• neutron → neutral
• electron → negative

charge of an atom is always neutral

same amount of protons and electrons

number of neutrons can vary and does not affect charge of atom.

• most of the atom’s volume is made up of empty space

empty space → parts of the atom not taken up by particles

Ions

• electrons are outside the nucleus and therefore can be moved more easily, electrons can also be transferred from one atom to another
• when neutral atom gains or loses electrons, number of protons stays the same
  • balance between positive and negative charge is lost → particle with an overall positive or negative charge → ion

ion → an atom or molecule with a net charge

• ion is represented by element symbol followed by overall charge in superscript

two types of ions:

1. negative ions
   1. forms when neutral atom gains electrons → more electrons than protons
   2. has a negative sign because it now has a negative charge as there are more electrons than protons
2. positive ions
   1. forms when neutral atom loses electrons → more protons than electrons
   2. has a plus sign because it now has a positive charge as there are more electrons than protons

electrical attraction

• electrons can be transferred between atoms by rubbing two objects together

Protons and electrons

atomic number → the number of protons in an atom

• all atoms of same element have the same number of protons → atomic number