Fundamental Ideas in Chemistry

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  • Created by: Hope
  • Created on: 06-06-13 19:21

Atoms

  • Atoms consist of electrons surrounding a nucleus that contains protons and neutrons
  • Neutrons are neutral 
  • Protons have a relative charge of +1
  • Electrons have a relative charge of -1
  • An element is a substance that is made of only one sort of atom

The Periodic Table:

  • In the periodic table the horizontal rows are called periods
  • The vertical columns are called groups
  • Elements in the same group have similar properties to eachother 

Metals and Non-Metals:

  • Metals are shown on the left of the periodc table 
  • Non-metals are shown on the right
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Atomic Structure

  • All substances are made from tiny particles called atoms.
  • An atoms has a small central nucleus made up of smaller sub-atomic particles called protons and neutrons.
  • The nucleus is surrounded by even smaller sub-atomic particles called electrons

Protons and electons have an electrical charge. Both have the same size of electrical charge, but the proton is positive and the electron negative. Neutrons are neutral.

The number of electrons in an atom is equal to the number of protons in its nucleus. This means atoms have no overall electrial charge.

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Atomic Number and Mass Number

  • The atomic number of an atom is the number of protons it contains
  • All the atoms of a particular element have the same atomic number (number of protons).
  • The atoms of different elements have different number of protons. E.g. All oxygen atoms have 8 protons and all sodium atoms have 11 protons.
  • The mass number of an atoms is the total number of protons and neutrons it contains. 
  • The mass number of an atom is never smaller than the atomic number. It can be the same but is usually bigger

Full Chemical Symbols

You need to be able to calculate the number of each sub-atomic particle in an atom is you are given its atomic number and mass number. The full chemical symbol for an element shows its mass number at the top, and its atomic number at the bottom.

This symbol tells you that the chlorine atom has 17 protons. It also has 17 electrons because the number of protons and electrons in an atom is the same. The symbol also tells you that the total number of protons and neutrons in the chlorine atom is 35. Neurons= 35-17=18 (http://www.bbc.co.uk/schools/gcsebitesize/science/images/gcsechem_84.gif)

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Electronic Structure

  • The electrons in an atom occupy energy levels. These are also called shells. Each electron in an atom is found in a particular energy level. 
  • The lowest energy level (innermost shell) fills with electrons first. 
  • Each energy level can only hold a certain number of electrons before it becomes full (first- 2, second- 8, third-8)

Working out an elements electronic structure

1) Find the element in the periodic table. Work out which period (row) it is in, and draw that number of circles around the nucleus.

2) Work out which group the element is in and draw that number of electrons in the outer circle-with eight for group 0 elements- except helium.

3) Fill in the other circles with as many electrons as needed. Remember -two in the first circle, and eight in the second and third circles.

4) Finally, check the number of electrons in the same as the atomic number.

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The Periodic Table

 A verticle column= Group(similar chemical properties) (http://www.bbc.co.uk/schools/gcsebitesize/science/images/38_modern_periodic_table.jpg)

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Group 1

The group 1 elements are found on the left hand side of the periodic table. They are called the alkali metals because they form alkaline compounds.

Their atoms all have one electron in their highest occupied energy level (outermost shell) This gives group 1 elements simialr chemical properties to eachother.

Reactions of group 1 elements with water

  • Lithium, sodium and potassium all react vigorously with water to form a metal hydroxide and hydrogen :
  • Metal + water > metal hydroxide + hydrogen
  • The metal hydroxides have strong alkalis 
  • The group 1 elements need to be stored under oil to prevent them reacting with oxygen and water vapour in the air

Reactions of group 1 elements with Oxygen 

Lithium, sodium and potassium are easily cut with a blade. The freshly cut surfaces are slivery and shiny, but quickly turn dull as the metal reactions with oxygen in the air. Group 1 metals react vigourously with oxygen to form metal oxides. 

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Group 0

The group 0 elemetns are found on the right hand side of the periodic table. They are called the noble gases because they are very unreactive.

The highest occupied energy levels (outermost shells) of their atoms are full:

  • Helium atoms have two electrons in their outer energy level 
  • Atoms of the other noble gases have eight electrons in their outer energy level.
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Reactions and Compounds

When elements react, their atoms join with other atoms to form compounds. Chemical bonds form when this happens which involves atoms transferring or sharing electrons.

New substances are formed by chemical reactions. When elements react together to form compounds their atoms join to other atoms using chemical bons. E.g. iron and sulfur react together to form a compound called iron sulfide.

Ionic Bonds 

Chemical bonds involve electrons from the reacting atoms. Compounds formed from metals and non-metals consist of ions. Ions are charged particles that form when atoms (or clusters of atoms) lose or gain electrons;

  • Metal atoms lose electrons to form positively charged ions 
  • Non metal atom gain electrons to form negatively charged ions 

Covalent Bonds

Compounds formed from non-metals consist of molecules. The atoms in a molecule are joined together by covalent bonds. These bonds form when atoms share pairs of electrons.

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Reactions and Compounds

When elements react, their atoms join with other atoms to form compounds. Chemical bonds form when this happens which involves atoms transferring or sharing electrons.

New substances are formed by chemical reactions. When elements react together to form compounds their atoms join to other atoms using chemical bons. E.g. iron and sulfur react together to form a compound called iron sulfide.

Ionic Bonds 

Chemical bonds involve electrons from the reacting atoms. Compounds formed from metals and non-metals consist of ions. Ions are charged particles that form when atoms (or clusters of atoms) lose or gain electrons;

  • Metal atoms lose electrons to form positively charged ions 
  • Non metal atom gain electrons to form negatively charged ions 

Covalent Bonds

Compounds formed from non-metals consist of molecules. The atoms in a molecule are joined together by covalent bonds. These bonds form when atoms share pairs of electrons.

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Chemical Formulas

The chemical formla of a compound shows how many of each type of atom join togehter to make up the compound. e.g. In Iron Sulfide every iron atom is joined to one sulfur atom, so we know its formula is FeS. 

In sodium oxide there are two sodium atoms for every oxugen atom. So we show its forumla and Na2O.

Sometimes you see more complex forumlae such as... 

 

  • a unit of Na2SO4 contains two sodium atoms, one sulfur atom and four oxygen atoms joined together
  • a unit of Fe(OH)3 contains one iron atom, three oxygen atoms and three hydrogen atoms - the brackets show that the 3 applies to O and H
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Chemical Equations

Copper and oxygen reaction: getting a balanced equation 

Balanced symbol equations show what happens to the different atoms in reactions. 

  • For example copper and oxygen react together to make copper oxide
  • Copper + Oxygen > Copper oxide

Copper and oxygen are the reactants becuse they are on the left of the arrow. Copper oxide is the product because it is on the right of the arrow. This is an unbalanced equation: Cu + O2 → CuO

There are unequal numbers of each type of atom on the left-hand side compared with the right-hand side. To make things equal you need to adjust the number of units of some of the substances until you get equal numbers of each type of atom on both sides.

2Cu + O2    →    2CuO - Now you see that there are two copper atoms and two oxygen atoms on each side.

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Conservation of Mass

No atoms are lost or made during a chemical reaction. This means that the mass is always conserved in other words the total mass of products after the reaction is the same as the total mass of the reactants at the start. 

This facts allows you to work out the mass of one substance in a reaction if the masses of the other substances are known e.g. 

  • Carbon reacts with oxygen to form carbon dioxide 
  • C + O2 → CO2
  • 12g of carbon will react to form 44g of carbon dioxide. It must react with 44 - 12 = 32 g of oxygen to do this 
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