Science - Chemistry: When Chemicals React

Chemistry When Chemicals React – How is the Periodic Table organised?

Elements are arranged by increasing atomic number, in rows called periods and columns called groups

Chemistry When Chemicals React – What does the period (row) of an element tell you?

The number of occupied electron shells

Chemistry When Chemicals React – What does the group (column) of an element tell you?

The number of electrons in its outer shell for main-group elements

Chemistry When Chemicals React – How can electron configuration identify an element's period?

Count the number of occupied electron shells; this gives the period

Chemistry When Chemicals React – How can electron configuration identify an element's group?

Count the outer-shell electrons; this identifies its group for main-group elements

Chemistry When Chemicals React – What group and period is an element with electron configuration 2,8,1?

Group 1 because it has 1 outer electron; Period 3 because it has 3 occupied shells

Chemistry When Chemicals React – What group and period is an element with electron configuration 2,8,7?

Group 17 because it has 7 outer electrons; Period 3 because it has 3 occupied shells

Chemistry When Chemicals React – What happens to metallic character across a period?

It generally decreases from left to right as atoms become less likely to lose electrons

Chemistry When Chemicals React – What happens to metallic character down a group?

It generally increases because outer electrons become further from the nucleus and easier to lose

Chemistry When Chemicals React – How does the reactivity of Group 1 metals change down the group?

It increases because the outer electron becomes easier to lose

Chemistry When Chemicals React – Why does Group 1 reactivity increase down the group?

Atoms become larger and shielding increases, so the nucleus attracts the outer electron less strongly

Chemistry When Chemicals React – How does the reactivity of Group 17 non-metals change down the group?

It generally decreases because atoms become less able to attract an extra electron

Chemistry When Chemicals React – Why does Group 17 reactivity decrease down the group?

Atoms become larger and shielding increases, making it harder to attract an extra electron

Chemistry When Chemicals React – How does non-metal reactivity generally change across a period?

It generally increases towards the halogens, which readily gain electrons

Chemistry When Chemicals React – How can periodic trends predict an element's reactivity?

Compare its group and position with other elements, then apply the known reactivity trend for that group

Chemistry When Chemicals React – What is an ion?

An atom or group of atoms with an electrical charge because it has gained or lost electrons

Chemistry When Chemicals React – What is a cation?

A positively charged ion formed when an atom loses electrons

Chemistry When Chemicals React – What is an anion?

A negatively charged ion formed when an atom gains electrons

Chemistry When Chemicals React – What is a polyatomic ion?

A group of bonded atoms that carries an overall electrical charge

Chemistry When Chemicals React – What is an ionic compound?

A compound made from positive and negative ions held together by electrostatic attraction

Chemistry When Chemicals React – How are ionic compounds formed?

Positive and negative ions attract each other, combining in ratios that produce an overall neutral compound

Chemistry When Chemicals React – How do you construct an ionic formula?

Combine the ions in the simplest whole-number ratio so their total positive and negative charges balance

Chemistry When Chemicals React – What is the formula of magnesium chloride?

MgCl₂; one Mg²⁺ balances two Cl⁻ ions

Chemistry When Chemicals React – What is the formula of aluminium oxide?

Al₂O₃; two Al³⁺ ions balance three O²⁻ ions

Chemistry When Chemicals React – What is the formula of calcium hydroxide?

Ca(OH)₂; one Ca²⁺ balances two OH⁻ ions

Chemistry When Chemicals React – What is the formula of sodium sulfate?

Na₂SO₄; two Na⁺ ions balance one SO₄²⁻ ion

Chemistry When Chemicals React – What is the formula of ammonium chloride?

NH₄Cl; NH₄⁺ and Cl⁻ balance in a 1:1 ratio

Chemistry When Chemicals React – Why are brackets used in some ionic formulas?

They show that more than one complete polyatomic ion is present

Chemistry When Chemicals React – How do you name a binary ionic compound?

Name the positive ion first, then the negative ion with its ending changed to -ide

Chemistry When Chemicals React – What does the ending -ide indicate?

A simple negative ion, usually formed from one non-metal element

Chemistry When Chemicals React – What does the ending -ate usually indicate?

A polyatomic ion containing oxygen

Chemistry When Chemicals React – How is NaCl named?

Sodium chloride

Chemistry When Chemicals React – How is MgO named?

Magnesium oxide

Chemistry When Chemicals React – How is CaCO₃ named?

Calcium carbonate

Chemistry When Chemicals React – How is Na₂SO₄ named?

Sodium sulfate

Chemistry When Chemicals React – What is a salt?

An ionic compound made from positive metal ions and negative non-metal or polyatomic ions

Chemistry When Chemicals React – What is the rate of a chemical reaction?

The change in concentration of a reactant or product per unit of time

Chemistry When Chemicals React – How can reaction rate be calculated?

Reaction rate = change in concentration ÷ time taken

Chemistry When Chemicals React – What is collision theory?

Particles must collide with enough energy and the correct orientation for a reaction to occur

Chemistry When Chemicals React – What is activation energy?

The minimum energy particles need for a successful reaction

Chemistry When Chemicals React – How does increasing temperature affect reaction rate?

Particles move faster, collide more frequently and more particles have enough energy to overcome activation energy

Chemistry When Chemicals React – How does increasing concentration affect reaction rate?

There are more particles in the same volume, causing more frequent collisions

Chemistry When Chemicals React – How does increasing surface area affect reaction rate?

More particles are exposed, allowing more frequent collisions

Chemistry When Chemicals React – How does a catalyst affect reaction rate?

It provides an alternative reaction pathway with lower activation energy, increasing the reaction rate

Chemistry When Chemicals React – Why does powdered calcium carbonate react faster than a large lump?

The powder has a greater surface area exposed to the acid, allowing more frequent collisions

Chemistry When Chemicals React – How can you investigate the effect of temperature on reaction rate?

Change temperature while keeping other variables constant, then measure how quickly the reaction occurs

Chemistry When Chemicals React – How can you investigate the effect of surface area on reaction rate?

Use different particle sizes of the same substance while keeping its mass and other conditions constant

Chemistry When Chemicals React – How can you investigate the effect of concentration on reaction rate?

Change concentration while keeping volume and other conditions constant, then measure reaction rate

Chemistry When Chemicals React – How can you investigate the effect of a catalyst on reaction rate?

Compare reaction rates with and without a catalyst while keeping other conditions constant

Chemistry When Chemicals React – What is the independent variable in an experiment?

The factor deliberately changed by the experimenter

Chemistry When Chemicals React – What is the dependent variable in an experiment?

The factor measured or observed to determine the effect of the independent variable

Chemistry When Chemicals React – What are controlled variables?

Factors kept constant to ensure a fair test

Chemistry When Chemicals React – What makes an experiment valid?

It measures what it is intended to measure and controls other factors that could affect the results

Chemistry When Chemicals React – What makes an experiment reliable?

Repeating trials and obtaining consistent results

Chemistry When Chemicals React – What makes an experiment accurate?

Measurements are close to the true or accepted value

Chemistry When Chemicals React – How can you improve the reliability of an experiment?

Repeat trials, identify anomalies and calculate an average

Chemistry When Chemicals React – How can you improve the accuracy of an experiment?

Use calibrated equipment, appropriate measuring instruments and careful measurement techniques

Chemistry When Chemicals React – What is a chemical equation?

A symbolic representation of a chemical reaction showing the reactants and products

Chemistry When Chemicals React – What are reactants?

The starting substances in a chemical reaction, written on the left side of an equation

Chemistry When Chemicals React – What are products?

The new substances formed during a chemical reaction, written on the right side of an equation

Chemistry When Chemicals React – What does the arrow in a chemical equation mean?

Reacts to produce or forms

Chemistry When Chemicals React – What is the Law of Conservation of Mass?

Mass cannot be created or destroyed during a chemical reaction

Chemistry When Chemicals React – Why must chemical equations be balanced?

Atoms are rearranged, not created or destroyed, so each element must have the same number of atoms on both sides

Chemistry When Chemicals React – What is the difference between a coefficient and a subscript?

A coefficient changes the number of particles; a subscript changes the number of atoms within a particle

Chemistry When Chemicals React – How do you balance a chemical equation?

Add coefficients in front of formulas until each element has the same number of atoms on both sides; never change subscripts

Chemistry When Chemicals React – How do you check whether an equation is balanced?

Count the atoms of each element on both sides and check that the numbers match

Chemistry When Chemicals React – What is the balanced equation for magnesium reacting with oxygen?

2Mg + O₂ → 2MgO

Chemistry When Chemicals React – What is the balanced equation for hydrogen reacting with oxygen to form water?

2H₂ + O₂ → 2H₂O

Chemistry When Chemicals React – How do you write a balanced equation from a word equation?

Replace substance names with chemical formulas, then add coefficients to balance each element

Chemistry When Chemicals React – What should you do when writing an equation from experimental observations?

Identify the reactants and products from the observations, write their formulas and balance the equation

Chemistry When Chemicals React – What does (s) mean in a chemical equation?

The substance is a solid

Chemistry When Chemicals React – What does (l) mean in a chemical equation?

The substance is a liquid

Chemistry When Chemicals React – What does (g) mean in a chemical equation?

The substance is a gas

Chemistry When Chemicals React – What does (aq) mean in a chemical equation?

The substance is dissolved in water

Chemistry When Chemicals React – What is a decomposition reaction?

A reaction in which one compound breaks down into two or more simpler substances

Chemistry When Chemicals React – What happens when copper carbonate is heated?

It decomposes into black copper oxide and carbon dioxide gas

Chemistry When Chemicals React – What is the word equation for the decomposition of copper carbonate?

Copper carbonate → copper oxide + carbon dioxide

Chemistry When Chemicals React – What is the balanced equation for the decomposition of copper carbonate?

CuCO₃ → CuO + CO₂

Chemistry When Chemicals React – What observations indicate that copper carbonate has decomposed?

The green copper carbonate turns black, and carbon dioxide gas is produced

Chemistry When Chemicals React – How can you test the gas produced when copper carbonate decomposes?

Pass it through limewater; it turns milky or cloudy, indicating carbon dioxide

Chemistry When Chemicals React – What safety precautions should be used when heating copper carbonate?

Wear safety glasses, use appropriate heating equipment and avoid inhaling dust or gases

Chemistry When Chemicals React – How do you write a word equation for another decomposition reaction?

Write the single reactant first, followed by an arrow and the simpler products formed

Chemistry When Chemicals React – What is a precipitation reaction?

A reaction in which two aqueous solutions react to form an insoluble solid called a precipitate

Chemistry When Chemicals React – What does soluble mean?

A substance that can dissolve in a particular solvent

Chemistry When Chemicals React – What does insoluble mean?

A substance that does not dissolve, or dissolves only very slightly, in a particular solvent

Chemistry When Chemicals React – What does aqueous mean?

A substance dissolved in water

Chemistry When Chemicals React – What is a solution?

A uniform mixture formed when a solute dissolves in a solvent

Chemistry When Chemicals React – What is a precipitate?

An insoluble solid formed during a chemical reaction between solutions

Chemistry When Chemicals React – How would particles appear in a diagram of a soluble substance?

The solute particles are spread evenly throughout the water

Chemistry When Chemicals React – How would particles appear in a diagram of an insoluble substance?

The substance remains as undissolved particles rather than spreading evenly through the water

Chemistry When Chemicals React – How would a precipitate appear in a particle diagram?

The newly formed insoluble particles appear as a solid, separate from the dissolved ions

Chemistry When Chemicals React – How can you identify whether a precipitate has formed?

The mixture becomes cloudy or a solid appears and may settle at the bottom

Chemistry When Chemicals React – How can solubility rules predict whether a precipitate forms?

Combine the ions and check the solubility of the possible products; an insoluble product forms a precipitate

Chemistry When Chemicals React – What happens when silver nitrate solution reacts with sodium chloride solution?

White silver chloride precipitate forms, while sodium nitrate remains dissolved

Chemistry When Chemicals React – What is the word equation for silver nitrate reacting with sodium chloride?

Silver nitrate + sodium chloride → silver chloride + sodium nitrate

Chemistry When Chemicals React – What is the balanced equation for silver nitrate reacting with sodium chloride?

AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

Chemistry When Chemicals React – How do you conduct a precipitation experiment?

Mix two ionic solutions, observe whether a solid forms, record observations and identify the products

Chemistry When Chemicals React – How do you write a word equation for a precipitation reaction?

Name the two aqueous reactants, then identify and name the products, including the insoluble precipitate

Chemistry When Chemicals React – What is corrosion?

The gradual deterioration of a metal due to chemical reactions with its environment

Chemistry When Chemicals React – What conditions are needed for iron to rust?

Both oxygen and water