The Structure of Matter (Bonding)

The Structure of Matter

(Bonding)

Types of Substance & Properties

All substances can be classified into one of these three types

Elements, compounds and mixtures

Element

1. A substance made of atoms that all contain the same number of protons (one type of atom) and cannot be split into anything simpler
2. There is a limited number of elements and all elements are found on the Periodic Table
3. Eg hydrogen, carbon, nitrogen

Compound

1. A pure substance made up of two or more elements chemically combined
2. There is an unlimited number of compounds
3. Compounds cannot be separated into their elements by physical means
4. Eg copper (II) sulphate (CuSO₄), calcium carbonate (CaCO₃), carbon dioxide (CO₂)

Mixture

1. A combination of two or more substances (elements and/or compounds) that are not chemically combined
2. Mixtures can be separated by physical methods such as filtration or evaporation
3. Eg sand and water, oil and water, sulphur powder and iron filings

Metals and nonmetals

1. The Periodic Table contains over 100 different elements
2. They can be divided into two broad types: metals and nonmetals
3. Most of the elements are metals and a small number of elements display properties of both types. These elements are called metalloids or semimetals

Properties of metals

1. Conduct heat and electricity
2. Are malleable and ductile (can be hammered and pulled into different shapes)
3. Tend to be lustrous (shiny)
4. Have high density and usually have high melting points
5. Form positive ions through electron loss
6. Form basic oxides 

Properties of nonmetals

1. Do not conduct heat and electricity
2. Are brittle and delicate when solid and easily break up
3. Tend to be dull and nonreflective
4. Have low density and low melting points (many are gases at room temperature)
5. Form negative ions through electron gain (except for hydrogen)
6. Form acidic oxides

Describing Alloys

1. Alloys are mixtures of metals, where the metals are mixed together but are not chemically combined
2. They can be made from metals mixed with nonmetals such as carbon
3. Alloys often have properties that can be very different to the metals they contain, for example they can have more strength, hardness or resistance to corrosion or extreme temperatures
4. Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms
5. This makes it more difficult for the layers to slide over each other, so they are usually much harder than the pure metal
6. Brass is a common example of an alloy which contains 70% copper and 30% zinc