Chemical Elements and Electrical Charges

A chemical element is a pure substance made of only one type of atom.
Each atom of an element has the same number of protons in its nucleus — this number is called the atomic number (Z).
For example:
• Hydrogen (H) has 1 proton → atomic number = 1
• Helium (He) has 2 protons → atomic number = 2
• Oxygen (O) has 8 protons → atomic number = 8
There are over 118 known elements in the periodic table, each with unique properties.

Structure of an Atom

An atom has three main particles:
1. Protons → positive charge (+1)
2. Electrons → negative charge (–1)
3. Neutrons → no charge (0)
They are arranged like this:
• Nucleus: contains protons and neutrons
• Electron cloud: electrons orbit around the nucleus

Electrical Charges in Atoms

In a neutral atom, the number of protons = electrons, so the charges cancel out.
Example:
Hydrogen atom → 1 proton (+1) and 1 electron (–1) → total charge = 0

Ions — When Atoms Gain or Lose Electrons

Atoms can gain or lose electrons to become ions, which carry electrical charge:
• Cation (+): Atom loses electrons → more protons than electrons
Example: Na → Na⁺ (sodium ion)
• Anion (–): Atom gains electrons → more electrons than protons
Example: Cl → Cl⁻ (chloride ion)

Isotopes — Same Element, Different Neutrons

Atoms of the same element can have different numbers of neutrons, forming isotopes.
Example: Hydrogen has three isotopes:
• Protium (¹H): 1 proton, 0 neutrons
• Deuterium (²H): 1 proton, 1 neutron
• Tritium (³H): 1 proton, 2 neutrons
All have the same electrical charge (neutral when un-ionized), but different atomic masses.

Table to help you identify Charges of Elements

Starting with Group I, elements have a positive charge. Look at the last digit in the number to determine the charge. Group 1 has a +1 charge. Group 2, +2. Skip the Transition Metals (Groups 3 – 12) because elements in that region may have a variety of charges. Group 13 has a +3 charge, and Group 14 may have a + or – 4 charge. Starting with Group 15, the charges are negative, starting with a -3 charge and decreasing to 0 by Group 18.

This information becomes important when you want to determine how elements combine with one another to form ionic bonds.