Topic 1: Atomic Structure and the Periodic Table

What is an atom?

The smallest part of an element that can exist.

What is a compound?

A substance made of two or more elements chemically combined in fixed proportions

How are mixtures different from compounds?

Mixtures aren’t chemically combined and can be separated by physical methods.

What did the alpha particle scattering experiment show?

Atoms have a small, dense, positively charged nucleus.

What are the charges of protons, neutrons, and electrons?

• Proton: +1

• Neutron: 0

• Electron: -1

What is the mass number of an atom?

The total number of protons and neutrons.

What is an isotope?

Atoms of the same element with different numbers of neutrons.

How is relative atomic mass calculated?

It’s the average mass of isotopes, taking into account their abundance.

How are electrons arranged in atoms?

In shells: 1st holds 2, 2nd holds 8, 3rd holds 8 (e.g. sodium = 2,8,1).

How are elements arranged in the modern periodic table?

By increasing atomic number.

Why did Mendeleev leave gaps in his periodic table?

For undiscovered elements and to keep elements with similar properties in groups.

What are group 1 elements called and how do they react with water?

Alkali metals; they react to form hydrogen gas and an alkaline solution.

How does reactivity change in group 1?

Reactivity increases down the group.

What are the group 7 elements called?

The halogens.

How does reactivity change in group 7?

Reactivity decreases down the group.

What is a displacement reaction in halogens?

A more reactive halogen displaces a less reactive one from its salt.

What are the group 0 elements called and why are they unreactive?

Noble gases; they have full outer electron shells.