Understanding Atoms, Isotopes, and Chemical Bonding

Atomic Structure and Isotopes

Proton number: The number of protons in an atom (and the number of electrons in an uncharged atom).
Nucleon number: The total number of protons and neutrons in an atom.

In the periodic table, moving one element to the right increases the proton number by 1. Moving one element down increases the proton number by 8 in the first three periods (excluding transition elements).

Isotopes and Radioactivity

Isotopes: Atoms of the same element that have different numbers of neutrons (e.g., Carbon-12 and Carbon-14).

• Non-radioactive isotopes: Stable atoms.
• Radioisotopes: Unstable atoms that decay and emit radiation.

Applications of Radioisotopes

• Medical: Cancer treatment (radiotherapy) using Cobalt-60 to kill cancer cells.
• Industrial: Tracers are added to oil or gas to detect leaks using a Geiger counter.
• Carbon Dating: Carbon-14 is used to estimate the age of organic matter by measuring remaining radiation levels.

Electron Configuration

Electrons are arranged in electron shells. Atoms react to achieve full outer shells (a full set of valency electrons). Noble gases are inert because they already possess full outer shells. The standard electron shell structure is 2, 8, 8, 18. Highly reactive elements have a stronger tendency to achieve a full outer shell, often forming more stable compounds.

Bonding and the Structure of Matter

Definitions

• Element: A substance that cannot be split into simpler substances via chemical reactions. Each element has a unique proton number.
• Mixture: Two or more elements mixed together but not chemically combined.
• Compound: A substance in which two or more different elements are chemically combined.

Properties of Metals

1. Strong.
2. Malleable and ductile.
3. Sonorous.
4. Good conductors of heat and electricity.
5. High melting and boiling points (except mercury).
6. High density.
7. React with oxygen to form basic metal oxides (note: aluminium oxide is amphoteric).
8. Form positive ions (cations) in reactions.
9. Some, such as iron, are magnetic.

Properties of Non-Metals

1. Brittle.
2. Lower melting and boiling points than metals.
3. Poor conductors of heat and electricity (except for graphite).
4. Low densities.
5. React with oxygen to form acidic oxides (note: carbon monoxide is neutral).
6. Form negatively charged ions (anions) in chemical reactions.

Alloys

An alloy is a mixture where at least one other substance is added to a metal to improve its properties. The additive is often another metal. For example, brass (70% copper and 30% zinc) is harder than pure copper, resists corrosion, and is used in musical instruments.