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Terms in this set (28)
How do you write the formula of metal elements, and why?
The formulae for metal elements are always written as an empirical formulae because metals exist as giant ionic lattices. You do not need to include numbers in their formulae because these would be huge, and would vary depending on the amount of metal.
How do you write the formula of non-metal elements, and why?
The non-metals in the group 0 exist as individual atoms, attracted to each other by weak intermolecular forces. Their formulae are the same as their chemical symbol. For example, Helium is He, and not He².
The non metals in the group 7 exist as diatomic molecules, attracted to each other by weak intermolecular forces. A diatomic molecule contains two atoms covalently bonded together. This means that all the elements in group 7 have a subscript 2 in them. Hydrogen, nitrogen and oxygen are not in group 7 but are also diatomic molecules.
Other non-metal elements exist as giant covalent structures, such as carbon or silicon, or as simple molecules. In chemical equations the formulae for all these elements are written in its empirical form. For example, sulphur exists as S⁸ molecules.
How do you write the formula of simple covalent compounds?
The molecular formula for a simple covalent compound consists of:
• The symbols for each element it contains
• The number of atoms of each element in one of its molecules.
Explain why the formulae for bromine is Br², and not Br
Bromine is in group 7, so exists as a diatomic molecule, which means it must contain a subscript 2.
State the forumulae for iodine, neon, phosphorus and zinc
Iodine - I2
Neon - Ne
Phosphorus - P4
Zinc - Zn
State the formulae for:
State the formulae for:
Hydrogen Flouride - HF
Caesium Bromide - CsBr
Strontium Oxide - SrO
State the definition of covalent bond
Covalent bond, in chemistry, the interatomic linkage that results from the sharing of an electron pair between two atoms.
How do you work out the formulae of common ions?
What is a Cation
A positive ion (an ion that has lost an electron).
What is an Anion
A negative ion (an ion that has gained an electron)
What is an Ion?
Ions are electrically charged particles formed when atoms lose or gain electrons . This loss or gain leaves a full outer shell, so the electronic structure of an ion is the same as that of a noble gas (such as helium, neon or argon).
How do you find the formulae of common ions?
The periodic table does not show you the formulae of ions, but you can work them out.
1. Hydrogen ions have a +1 charge
2. Metals in group 1, 2 and 3 produce positive ions in which the number of charges is the same as their group number.
3. Transition metals are in the block of elements between groups 2 and 3. They produce positive ions that usually have a 2+ charge.
4. Non-metals in groups 5, 6 and 7 produce negative ions in which no. of charges are equal to 8 minus the number of the group (eg, group 7's charge is 1-)
Compound ions are ions that contain more than one element.
State the formulae of every positive compound ion
Ammonium - NH₄⁺
State the formulae of every negative compound ion
Hydroxide - OH⁻
Nitrate - NO³-
Carbonate - CO₃²⁻
Sulfate - SO₄²⁻
How do you write for the formulae for ionic compounds?
In any ionic compound, the total number of positive charges must equal the total number of negative charges. This is easy to see when the ions involved have the same number of charges. It can be more difficult when they have different numbers of charges
What is the law of conservation of mass?
The Law of Conservation of Mass is the discovery that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction.
What is an experiment to show the conservation of mass?
You can investigate conservation of mass by carrying out a reaction in a closed system. This is a container in which no substances can enter or leave during a reaction.
1. A beaker of reactants in a solution where the products are not gases
2. A flask attached to a gas syringe to stop products in the gas state escaping.
Why does mass seem to change during reactions
Substances can leave or enter the reaction mixture in a non-enclosed system. This usually happens in an open container when the reaction involves a substance in the gas state. For example, magnesium reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen. Hydrogen then escapes because it is in the gas state, so the mass appears to go down during the reaction.
The mass may appear to go up during a reaction, such as when metal reacts with oxygen in the air. The metal atoms combine with the oxygen atoms from the air to form a metal oxide in the solid state. If you could measure the mass of oxygen atoms used, you would find that the total mass before the reaction would be equal to the total mass after.
How do you calculate masses?
2.40g of magnesium is heated in the air . It forms 4.00g of magnesium oxide. Calculate the mass of oxygen gained.
Write down what you know using the law of conservation of mass.
mass of magnesium + mass of oxygen = mass of magnesium oxide
If necessary, rearrange the equation and substitute the masses given.
mass of oxygen = mass of magnesium oxide - mass of magnesium
mass of oxygen = 4.00g - 2.40g
What are balanced equations?
A word equation is a simple model for a chemical reaction. It shows the names of the reactants and the products involved. A balanced equation is a more detailed model. It shows:
1. How the atoms are rearranged in a reaction
2. The relative amounts of each substance involved
For example, when carbon reacts with oxygen to create carbon dioxide:
C + O₂ = CO₂
The equation shows that one carbon atom reacts with one oxygen molecule to produce one carbon dioxide molecule. It models in symbols what happens to the atoms in the reaction (see below)
C + O O ---> O C O
Sulfur reacts with oxygen to form sulfur dioxide: S + O₂ --> SO₂. Describe what the equation shows.
The equation shows that one sulfur atom reacts with one oxygen molecule to produce one sulfur dioxide molecule.
How do you write balanced equations?
Na + O₂ --> NaO₂ is not balanced: The numbers of atoms on each side are not equal.
4Na + O₂ --> 2NaO₂ is balanced; on each side there is four atoms of Na and two of O
Step by Step:
One stage in the manufacturing of titanium involves reacting titanium chloride with magnesium, producing titanium and magnesium chloride. Write a balanced equation for the reaction.
Write the word equation (if you are not given it) and write the formula for each substance underneath.
titanium chloride + magnesium = titanium + magnesium chloride
TiCl₄ + Mg --> TiMgCl₂
Add numbers on the left of one or more formulae, if necessary, making equal numbers of atoms on each side
TiCl₄ + 2Mg --> Ti + 2MgCl₂
What are state symbols?
State symbols represent the state of each reactant and each product in a reaction, and must be included in every chemical equation.
eg: (g), (s), (l)
What are half equations?
A half equation is the model for the change that happens to one reactant in a chemical reaction.
The balanced equation for the reaction between sodium and chlorine is:
2Na(s) + Cl₂(g) --> 2NaCl(s)
Sodium chloride, NaCl, is an ionic compound that contains Na+ ions and Cl⁻ ions. Sodium ions form when sodium atoms lose electrons. This half equation models the change.
Na --> Na⁺ + e⁻
Chloride ions form when chlorine atoms gain electrons. However, chlorine atoms are joined together by covalent bonds to make diatomic chlorine molecules, so this is the half equation that models the change:
Cl₂ + 2e⁻ --> 2Cl⁻
Notice that you must balance the charges in half equations, not just the numbers of atoms and the ions they form.
Magnesium, Mg, reacts with oxygen, O₂, to produce magnesium oxide, MgO. Magnesium oxide contains Mg²⁺ ions and O²⁻ ions. Write two half equations to model the reaction.
Mg --> Mg²⁺ + 2e⁻
O₂ --> O²⁻ + 2e⁺
What are ionic equations?
A complete ionic equation shows the ions present in a reaction mixture. It usually also includes the formulae of any molecular substances present, or substances in their solid state. For example, dilute hydrochloric acid reacts with sodium hydroxide solution to produce sodium chloride solution and water:
HCl(aq) + NaOH(aq) --> NaCl(aq) + H₂O(I)
This ionic equation also models the reaction:
H⁺(aq) + Cl⁻(aq) + OH⁻(aq) --> Na⁺(aq) + Cl⁻(aq) + H₂O(I)
Water is a molecular substance so it is modelled as H₂O.
Notice that Cl⁻ ions and Na⁺ ions appear in the same form on both sides of the equation. They are called spectator ions because they are in the reaction mixture but do not take part in the reaction. A net ionic equation leaves out the spectator ions. In this example, the ionic equation becomes:
H⁺(aq) + OH⁻(aq) --> H₂O(I)
What does (aq) mean?
'Aqua', or 'dissolved in water'
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