Particles in atoms
Protons, neutrons and electrons are called SUBATOMIC PARTICLES. You can work out how many of each type of subatomic particle an atom has from its atomic number and mass number.
The number of protons in an atom of an element is called its ATOMIC NUMBER.
The atoms of different elements have different numbers of protons - no two elements can have the same atomic number.
Number of electrons
Atoms have no overall charge. This is because the number of electrons in an atom is the same as the number of protons.
The total number of protons and neutrons in an atom is called its MASS NUMBER.
The number of protons is goven by the atomic number, which is 11 for sodium, for exxample
You should be able to represent the electronic structure of the first 20 elements.
The electrons in an atom occupy different ENERGY LEVELS around the nucleus. Each electron in an atom is at particular energy level. Electrons occupy the lowest available energy levels.
Energy leveks are also called SHELLS:
- The innermost shell is the lowest energy level.
- The outer shell is the highest occupied energy level.
Electronic structure and groups
Atoms of the elements in a group in the periodic table have the same number of electrons in their highest energy level (outer shell). This gives the elements similar chemical properties.
Group 1 (alkali metals)
The elements in Group 1 include lithium, sodium and potassium. Their atoms all have just one electron in their highest occupied energy level (outer shell).
When elements react with each other, their atoms join together to form COMPOUNDS.
Metals and non-metals react together to form compounds. The compounds are made of IONS.
An ion is a charged particle formed when an atom, or group of atoms, loses or gains electrons.
Giving and taking electrons
We use word equations and balanced symbol equations to represent chemical reactions.
In a chemical reaction:
- REACTANTS are the substances that react together
- PRODUCTS are the substances made.
In a WORD EQUATION, two or more reactants or products are seperated by a + sign.
LIMESTONE is a type of rock. It is mostly calcium carbonate, CaCO3.
Uses of limestone
- As raw material for making cement, mortar and concrete.
- As blocks and slabs for walls and pavements.
- As AGGREGATE (small lumps) for the base of roads and railways.
Calcium carbonate chemistry
Many metal carbonates break down when they are heated. The reaction is called THERMAL DECOMPOSITION.
metal carbonate -------> metal oxide + carbon dioxide
When calcium carbonate is heated, it decomposes to form calcium oxide and carbon dioxide:
These carbonates decompose in a similar way to calcium carbonate when heated:
- magnesium carbonate
- zinc carbonate
- copper carbonate
Not all carbonates of metals in Group 1 decompose when heated with a Bunsen flame.
Unreactive metals such as gold are found in the Earth's crust as the metal element itself. However, most metals are found as compounds. These need chemical reactions to extract them from their ores.
Rocks contain metals or their compounds. An ORE is a rock that contains enough of a metal to make its extraction economical.
Rocks may contain too little metal to make extraction worthwhile (if the cost of extracting the metal is greater than the value of the metal itself). Over time, metal prices may rise and these LOW-GRADE ORES may become useful.
Iron is extracted from iron oxide in a blast furnace by reaction with carbon:
High-grade copper ores contain a high proportion of copper compounds.
Copper is extracted from these ores by SMELTING. This involves heating copper ores in a furnace. For example, copper sulphide is heated in air to produce copper:
Copper is purified by ELECTROLYSIS.
Recycling metals instead of extracting them from ores has many benefits.
Extracting metals from their ores:
- uses up limited resources
- uses a lot of energy
- damages the environment
Recycling metals reduces these disadvantages. Used metal items are collected. Rather than throwing them away, these are taken apart. The metal is melted down to make new items.
Recycling metals means:
- metal ores will last longer
- less energy needed to recycle metals than to mine ores and extract metals
- fewer quarries and mines needed