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
- A substance made of atoms that all contain the same number of protons (one type of atom) and cannot be split into anything simpler
- There is a limited number of elements and all elements are found on the Periodic Table
- Eg hydrogen, carbon, nitrogen
Compound
- A pure substance made up of two or more elements chemically combined
- There is an unlimited number of compounds
- Compounds cannot be separated into their elements by physical means
- Eg copper (II) sulphate (CuSO4), calcium carbonate (CaCO3), carbon dioxide (CO2)
Mixture
- A combination of two or more substances (elements and/or compounds) that are not chemically combined
- Mixtures can be separated by physical methods such as filtration or evaporation
- Eg sand and water, oil and water, sulphur powder and iron filings
Metals and nonmetals
- The Periodic Table contains over 100 different elements
- They can be divided into two broad types: metals and nonmetals
- 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
- Conduct heat and electricity
- Are malleable and ductile (can be hammered and pulled into different shapes)
- Tend to be lustrous (shiny)
- Have high density and usually have high melting points
- Form positive ions through electron loss
- Form basic oxides
Properties of nonmetals
- Do not conduct heat and electricity
- Are brittle and delicate when solid and easily break up
- Tend to be dull and nonreflective
- Have low density and low melting points (many are gases at room temperature)
- Form negative ions through electron gain (except for hydrogen)
- Form acidic oxides
Describing Alloys
- Alloys are mixtures of metals, where the metals are mixed together but are not chemically combined
- They can be made from metals mixed with nonmetals such as carbon
- 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
- Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms
- This makes it more difficult for the layers to slide over each other, so they are usually much harder than the pure metal
- Brass is a common example of an alloy which contains 70% copper and 30% zinc
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