What are the three subatomic particles and their charges?

protons - +1 electrons - -1 neutrons - 0

How do you determine the number of protons, neutrons, and electrons in an atom?

Protons = Atomic number Electrons = Atomic number (for a neutral atom) Neutrons = Mass number − Atomic number

How do you draw an atom?

Draw a nucleus containing protons and neutrons. Add electron shells. Fill shells

What is the history of the atomic model?

John Dalton – atoms are tiny solid spheres. J. J. Thomson – discovered electrons. Ernest Rutherford – nucleus discovered. Niels Bohr – electrons in shells. James Chadwick – discovered neutrons.

What did Rutherford's alpha scattering experiment show?

Most of the atom is empty space. Positive charge is concentrated in a tiny nucleus. The nucleus contains most of the atom's mass.

What is an isotope?

Have the same number of protons. Have different numbers of neutrons.

How do you calculate relative atomic mass (Ar)?

Ar​=(35×75)+(37×25)​=35.5 100

Why are elements in the same group chemically similar?

They have the same number of electrons in their outer shell. These outer electrons determine how an element reacts.

What happens to reactivity in Group 1

Outer electron is further from the nucleus. Attraction between nucleus and electron becomes weaker. Electron is lost more easily.

What happens when alkali metals react with water?

Metal + Water → Metal Hydroxide + Hydrogen

What happens to reactivity in Group 7

More electron shells. Greater shielding. Harder to gain an electron.

What are the properties of halogens?

Non-metals Coloured Exist as diatomic molecules Gain one electron when reacting

Why are noble gases unreactive?

they are inert

How do you balance chemical equations?

Count atoms on each side. Change only the large numbers (coefficients). Never change the small numbers in formulas. Check all atoms balance.

Quick Memory Check

Group 1: Reactivity increases down the group. Group 7: Reactivity decreases down the group. Group 0: Full outer shell → unreactive. Isotopes: Same protons, different neutrons. Relative atomic mass: Weighted average of isotopes. Balancing equations: Change coefficients only, never formulas.