Year_9_summer_assessment_knowledge_organisers

Diet and Nutrition

The contents of a healthy human diet include carbohydrates, lipids (fats and oils), protein, vitamins, minerals, dietary fiber, and water.
A balanced diet includes all the nutrients the body needs in the right quantities.
Carbohydrates provide energy and are found in foods like bread, potatoes, rice, and pasta.
Lipids (fats) provide energy and insulation and are found in nuts, dairy, meat, oils, and sweets.
Proteins are for growth and repair of cells and tissues and are found in eggs, pulses, fish, meat, nuts, and dairy products.
Vitamins and minerals are essential for processes in the body and are plentiful in fruit and vegetables, but provided by all parts of the diet.
Calcium is a mineral used in making bones and teeth.
Fiber adds bulk to food and helps it pass through the digestive system and is found in fruit, vegetables, and wholegrain cereals.
Water allows transport of substances around the body and for chemical reactions in cells.
Malnutrition occurs when a person does not have a balanced diet.
Imbalances in the diet can result in health consequences, including obesity, starvation, and deficiency diseases.

Food Tests

Iodine solution changes from brown to black in the presence of starch.
Benedict’s reagent changes from blue to orange/red when heated in the presence of simple sugars like glucose.
Biuret reagent changes from blue to purple in the presence of protein.

The Digestive System

The digestive system breaks down molecules in food into soluble substances for absorption and use by cells.
Food passes through the mouth, esophagus, stomach, small intestine, large intestine, and rectum.
Mechanical digestion is the physical cutting, squashing, and churning of food, e.g., by teeth or the stomach.
Chemical digestion is when enzymes and other chemicals are used to speed up reactions.
In the mouth, mechanical and chemical digestion occur.
Salivary glands secrete enzymes that begin chemical digestion.
The esophagus moves food into the stomach.
In the stomach, mechanical and chemical digestion occur, and the stomach contains acid.
Water is absorbed into the bloodstream from the large intestine.
Undigested food leaves the digestive system via the anus.
Bile is made in the liver and stored in the gall bladder. Bile is alkaline and neutralizes the acid in the stomach.

The Small Intestine

Chemical digestion takes place in the small intestine and small, soluble molecules move into the bloodstream by diffusion.
The small intestine is well adapted because it has many villi, which increase the surface area to increase diffusion of nutrient molecules into the blood, and also a good blood supply.

Enzymes

Enzymes speed up chemical reactions in the body.
Digestive enzymes break down large nutrient molecules into smaller molecules that can be absorbed into blood and used by cells.
Carbohydrases (e.g., amylase) break down carbohydrates into simple sugars.
Lipases break down lipids into glycerol and fatty acids.
Proteases break down proteins into amino acids.
The lock and key theory models how enzymes work, having an active site with a specific shape to the substrate it joins to.

Plant Nutrition

Plants require minerals for healthy growth.
Plants need nitrates to make proteins for growth.
Plants need magnesium to make chlorophyll.
Plants get magnesium and nitrates from the soil via their roots.
Plants can be damaged by deficiencies; a magnesium deficiency affects photosynthesis.

Eukaryotes and Prokaryotes

Eukaryotic cells have membrane-bound organelles and genetic material in the nucleus.
An organelle is a part of a cell that carries out a specific function.
Plant and animal cells are examples of eukaryotic cells, typically between 10-100 \mu m in size.
All eukaryotic cells have a nucleus, mitochondria, ribosomes, cytoplasm, and a cell membrane. Plant cells also have a cell wall, vacuole, and chloroplasts.
Mitochondria are the site of aerobic respiration, which releases energy for cellular processes.
Ribosomes are the site of protein synthesis.
Prokaryotic cells do not contain membrane-bound organelles and are approximately 10 orders of magnitude smaller than eukaryotic cells.
Prokaryotic cells contain genetic material in small rings called plasmids or in larger loops.
Prokaryotic ribosomes are smaller than eukaryotic ribosomes.

Growing Microorganisms

Petri dishes are used to produce cultures of bacteria and other micro-organisms.
Cultured bacteria are grown on a nutrient medium in controlled conditions.
Aseptic techniques must be used to prepare cultures to prevent contamination and the growth of harmful bacteria.
Petri dishes, inoculating loops, and culture media must be sterilized before use; a flame can sterilize equipment.
An inoculating loop transfers bacteria to the petri dish.
The lid of a Petri dish should be partially secured with tape to keep bacteria in, but allow aerobic conditions.
The Petri dish must be stored upside down to prevent condensation affecting bacterial growth.
In school laboratories, cultures should generally be incubated at 25 \,^{\circ}C to prevent the growth of harmful bacteria.
A cotton wool swab can transfer a sample to a Petri dish to investigate bacterial growth.
Bacteria on a Petri dish divide rapidly while the nutrient supply is rich. Every time the bacteria reproduce, the number doubles.
The total number of bacteria can be calculated using the formula: Final\ number \, of \, bacteria = Initial \, number \, of \, bacteria \times 2^{number \, of \, divisions}

Microscopy

Microscopy uses microscopes to view samples that cannot be seen with the naked eye.
Light microscopes allow viewing of the largest organelles, including the nucleus, cell membrane, cell wall, and cytoplasm. A stain is often used to make the organelles clearer.
The parts of a light microscope include the eyepiece lens, objective lenses, stage, coarse focusing wheel, fine focusing wheel, light/mirror.
A sample used with a light microscope must be very thin to allow light to pass through.
The total magnification of a microscope can be calculated using the following equation: Total\, magnification = Objective \,lens \times Eyepiece \,lens
Electron microscopes have a greater magnification and resolution than light microscopes but are much more expensive.
Magnification is the number of times larger an image is than the object.
Resolution is the ability to distinguish between two points.
Electron microscopes allow us to see more organelles and study cells in greater detail.
Magnification can be calculated using:
A scale bar can be used to calculate the magnification of an irregular object.
Magnification does not have a unit because it is a ratio.

Transport of Substances

Diffusion is the spreading out of particles of a gas or liquid, resulting in net movement from an area of high concentration to low concentration.
In gas exchange, oxygen and carbon dioxide diffuse between the alveoli and the blood.
The rate of diffusion is increased by:
- an increase in temperature
- an increase in the difference in concentrations (concentration gradient)
- a greater surface area
Unicellular organisms have a relatively high surface area to volume ratio, allowing sufficient transport of all required substances.
Large, multicellular organisms have adaptations to increase the surface area to volume ratio to allow for efficient exchange of substances.
Osmosis is the diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane.
A partially permeable membrane lets particular substances pass through it, either into or out of the cell.
A hypertonic solution has a higher concentration of solute than the cell. Water always moves out of a cell in a hypertonic solution, causing it to shrivel or become flaccid.
Tissue placed in hypertonic solutions decreases in mass.
A hypotonic solution has a lower concentration of solute than the cell. Water always moves into a cell in a hypotonic solution, causing it to swell or become turgid.
Tissue placed in hypotonic solutions increases in mass.
An isotonic solution has the same concentration of solute as the cell. Water will not move in or out of cells in an isotonic solution, so their size will stay constant.
Guard cells open and close due to the movement of water by osmosis.
The mass of plant tissue can be measured before and after being placed in a solution of known concentration to calculate the percentage change in mass due to osmosis.
Active transport moves substances from a more dilute solution to a more concentrated solution, requiring energy from respiration.
Active transport works against the concentration gradient.
Active transport is used in root hair cells to absorb mineral ions from the soil that are essential for plant growth.

Cell Division and Differentiation

Both eukaryotic and prokaryotic cells undergo cell division.
Cells increase in number by dividing into two.
The eukaryotic cell cycle contains a growth phase where the cell grows to double sub-cellular structures (such ribosomes and cell membrane) and DNA, then the cell splits into two during mitosis.
The length of time in a certain stage of the cell cycle can be calculated using the following formula:
The mass of DNA in a cell doubles during the growth phase of the cell cycle.
During mitosis, DNA (arranged into chromosomes) is pulled to separate ends of the cell ready for division.
The final part of the cell cycle is when the cell membrane splits to produce two identical daughter cells.
Mitosis is used by eukaryotic organisms for growth and repair and by those that reproduce asexually.
Mitosis does not occur in prokaryotic cells because they do not possess a nucleus.
Checkpoints in the cell cycle control the rate of cell division.
Cancer is caused by uncontrolled cell division.
A tumor is a mass of cells caused by uncontrolled cell division.
Benign tumors are a mass of cells contained in one area.
Malignant tumors are formed of cancer cells that invade other tissues and spread around the body where they form secondary tumors.
A risk factor is a gene or lifestyle choice that can increase the likelihood of a person developing a disease.
Lifestyle risk factors for cancer include poor diet, lack of exercise, smoking, UV exposure.
Genetic risk factors for cancer include gene mutations.
Specialized cells arise from stem cells.
Stem cells are cells that are capable of differentiating into other types of cell.
When a cell differentiates, it acquires specific structures needed for that cell type.
Most animal cells differentiate at an early stage of development.
Embryonic stem cells can differentiate into all human cell types.
Adult bone marrow contains stem cells that can differentiate into different types of blood cell.
Embryonic stem cells can be used to study and treat diseases. There are religious and ethical objections to using embryonic stem cells in scientific research.
Plants contain meristem tissue at the tips of shoots and roots that retains the ability to differentiate throughout a plant’s life.

Biodiversity

Biodiversity is the variety of different species in an ecosystem.
Biodiversity can be measured by using sampling techniques to count the abundance of different species.
A quadrat is a piece of equipment (a frame) used to count the abundance of species.
Random sampling is used to measure the abundance of a species in a particular habitat, using quadrats placed at random coordinates.
Systematic sampling is used to measure the effect of a factor on the distribution of a species, using a transect with quadrats placed at regular intervals.
High biodiversity makes an ecosystem stable because each species is not dependent on just one other.

How Humans Affect Biodiversity

Many human activities are reducing biodiversity on Earth.
The global population is increasing, so more resources are needed and more waste is being produced.
Pollution is caused when waste is not properly treated.
Pollution can be very harmful to plants and animals and reduce biodiversity.
Pollution does not always affect all species equally, as some may be more resistant.
Biodiversity is reduced by humans using land for building, quarrying, farming, and waste disposal.
Peat from peat bogs is used for compost for gardens and farms, destroying habitats.
Scientists and other citizens are using different methods to counteract some of the negative impacts of humans on biodiversity:
- Protecting rare habitats
- Maintaining nature reserves
- Breeding programs for endangered species
- Recycling resources to reduce landfill waste
- Reducing deforestation
- Growing hedgerows on farms to allow more crops to grow

Global Warming

Levels of carbon dioxide and methane (greenhouse gases) in the atmosphere are increasing, contributing to global warming.
Human activities contribute to greenhouse gas emissions, particularly the burning of fossil fuels in industry and transport.
There are many biological consequences of global warming including:
- Melting polar ice caps
- Rising sea levels
- Extreme weather patterns
- Flooding
- Loss of habitats

Human Waste

The increasing human population means that more resources are required and more waste is produced.
More waste is also produced through the improved standard of living.
If waste is not treated properly it results in pollution:
- Water pollution is caused by poor sewage treatment and leaching of fertilizers
- Air pollution is caused by smoke and acidic gases
- Land pollution is caused by landfill and toxic chemical waste

Pyramids of Biomass

Biomass is lost between trophic levels in a food chain.
Producers (mostly plants and algae) transfer about 1% of the light energy they absorb for photosynthesis.
Only approximately 10% of biomass from each trophic level is transferred to the level above.
Biomass is lost through waste (faeces, urine, sweat, gas) and through life processes such as movement and thermoregulation.

Farming and Biotechnology

Efficiency of food production (between trophic levels) can be improved by restricting energy transfer from food animals to the environment.
This includes intensive farming methods where movement of animals is limited and the temperature of their surroundings is controlled.
Fish stocks in oceans are declining because of overfishing.
Fish stocks need to remain at a high enough level for breeding to occur, to prevent the disappearance of some species.
Fishing quotas are used to ensure that ocean fish stocks remain at a sufficient level and net sizes can be restricted to prevent juvenile fish being caught, so they can then have their own offspring.
Modern biotechnology allows large quantities of microorganisms to be cultured for food.
Fusarium fungus is used to produce mycoprotein (Quorn), a protein-rich food suitable for vegetarians.
Fusarium is grown on glucose syrup in aerobic conditions before being harvested and purified.
Genetically modified (GM) bacterium can be used to produce insulin to be harvested and purified to treat people with diabetes.
GM crops, such as golden rice, can be used to provide increased nutritional value in areas where it is lacking.

Food Security

Food security is having enough food to feed a population.
Many factors can threaten food security:
- Increasing birth rate means there is not enough food for the growing population
- Changing diets in developed countries means that scarce food resources are being transported across the world
- New pests and pathogens are affecting farming
- Environmental changes, including droughts, which can lead to famines
- Political instability and conflicts in some parts of the world threaten access to food and water
Sustainable methods must be found and used to feed Earth’s population.

Meiosis

Cells in reproductive organs divide by meiosis to form gametes.
Meiosis halves the number of chromosomes in gametes.
When a cell divides in meiosis: copies of the genetic information are made and the cell then divides twice to form four gametes, each with a single set of chromosomes. This makes the gametes genetically different from each other.
Gametes join at fertilization to form a zygote with the normal number of chromosomes.
After fertilization, the new cell divides by mitosis and the number of cells increases. As the embryo develops, cells differentiate.

Types of Reproduction

Organisms use either sexual or asexual reproduction to reproduce.
Sexual reproduction involves the joining (fusion) of male and female gametes:
- sperm and egg cells in animals
- pollen and egg cells in flowering plants
- In sexual reproduction there is mixing of genetic information which leads to variety in the offspring.
Asexual reproduction involves only one parent and no fusion of gametes. There is no mixing of genetic information so this leads to genetically identical offspring (clones).

DNA, Genes, and Chromosomes

DNA is a polymer made of two strands which form a double helix.
The DNA is contained in structures called chromosomes.
A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids to make a specific protein.
The genome of an organism is the entire genetic material of that organism.
Every chromosome is one of a pair so there are two copies of each gene in every genome.
Different versions of genes are called alleles.

Inheritance

Some characteristics, for example fur color in mice or red-green color blindness, are controlled by one gene.
The set of particular alleles present is called the genotype. The genotype (e.g., brown allele of the fur color gene) is expressed to make the phenotype (e.g., brown fur).
A dominant allele is always expressed when present even when only one copy is present. A recessive allele is only expressed when there are two copies of it (i.e., no dominant allele).
If the two alleles present are the same, either both dominant or both recessive, then this is described as homozygous. If one allele is dominant and one is recessive then this is described as heterozygous.
Most characteristics are the result of the interaction of many genes.
Punnett square diagrams can be used to predict the genotypes of offspring. Capital letters are used to denote dominant alleles and lower-case letters are used to denote recessive alleles.

Inherited Disorders

Polydactyly is an inherited disorder where sufferers have extra digits; it is caused by a dominant allele.
Cystic fibrosis is an inherited disorder where sufferers have lung problems due to a faulty cell membrane protein; it is caused by a recessive allele.
An individual can be a carrier of a recessive disorder, but not of a dominant disorder.
Family trees show over several generations which individuals had a particular phenotype. This can be used to derive the genotype.

Sex Determination

Ordinary human body cells contain 23 pairs of chromosomes. 22 pairs control characteristics only, but one of the pairs carries the genes that determine sex.
In females the sex chromosomes are the same (XX). In males the chromosomes are different (XY).
There are advantages to sexual reproduction:
- It produces variation in the offspring
- If the environment changes variation gives a survival advantage by natural selection
There are also advantages to asexual reproduction:
- Only one parent is needed
- It is more time and energy efficient as organisms do not need to find a mate
- It is faster than sexual reproduction
- Many identical offspring can be produced when conditions are favorable
Some organisms reproduce by both methods depending on the circumstances. Malarial parasites reproduce asexually in the human host but sexually in the mosquito. Many fungi reproduce asexually by spores but also reproduce sexually to give variation. Many plants produce seeds sexually, but also reproduce asexually by runners (e.g., strawberry plants) or bulb division (e.g., daffodils).

Development of Understanding Genetics

Our current understanding of genetics has developed over time. In the mid-19th century Gregor Mendel carried out breeding experiments on plants and observed that the inheritance of each characteristic is determined by ‘units’ that are passed on to descendants unchanged. The importance of Mendel's discovery was not recognized until after his death.
In the late 19th century the behavior of chromosomes during cell division was observed. In the early 20th century it was observed that chromosomes and Mendel’s ‘units’ behaved in similar ways, leading to the idea that the ‘units,’ now called genes, were located on chromosomes.
A karyotype diagram can be used to display the chromosomes of an individual.
In the mid-20th century the structure of DNA was determined and the mechanism of gene function worked out. This scientific work by many scientists led to the gene theory being developed. Watson, Crick, Wilkins, and Franklin played a part in the development of the DNA model.

DNA and Protein Synthesis

The monomers of DNA are called nucleotides. The DNA polymer is made up of repeating nucleotide units.
The long strands of DNA consist of alternating sugar and phosphate sections. Attached to each sugar is one of the four bases. In the complementary strands, a C is always linked to a G on the opposite strand and a T to an A.
A sequence of three bases is the code for a particular amino acid. The order of bases controls the order in which amino acids are assembled to produce a particular protein.
Proteins are synthesized on ribosomes, according to a template. Carrier molecules bring specific amino acids to add to the growing protein chain in the correct order. When the protein chain is complete it folds up to form a unique shape, enabling the proteins to do their job as enzymes, hormones or forming structures in the body such as collagen.
Mutations occur continuously. Most do not alter the protein, or only alter it slightly so that its appearance or function is not changed. A few mutations code for an altered protein with a different shape. An enzyme may no longer fit the substrate binding site or a structural protein may lose its strength.
A change in DNA structure may result in a change in the protein synthesized by a gene.

Rock Cycle

Magma and lava are molten (melted, very hot liquid) rock.
Magma is molten rock underground.
Lava is molten rock above ground.
When molten rock cools it solidifies to form igneous rocks.
Igneous rocks formed from magma underground are intrusive rocks.
Intrusive rocks cool slowly and have large crystals (e.g., granite).
Igneous rocks formed from lava above ground are extrusive rocks.
Extrusive rocks cool quickly and have small crystals (e.g., obsidian).
Rocks can be broken down into small pieces by weathering.
Weathering can be physical (e.g., water getting into cracks and expanding when it freezes, forcing the crack wider).
Weathering can be chemical (e.g., acid rain reacting with the rock to make salts).
Weathering can be biological (e.g., tree roots forcing cracks wider).
Erosion is the movement of pieces of rock away from where they started.
Erosion can involve the wind, flowing water or ice, and gravity.
When pieces of rock sink to the bottom of lakes or seas they form layers of sediment. This is sedimentation.
Layers of sediment build up in layers and the bottom layer becomes compressed.
Dissolved minerals fill any spaces and bind rock particles together; this is cementation.
Sedimentation, compression, and cementation form sedimentary rocks (e.g., chalk or sandstone).
If rocks are pushed deep underground, they experience tremendous heat and pressure.
Heat and pressure change the structure of igneous and sedimentary rocks to form metamorphic rocks (e.g., marble formed from chalk).
The formation of rocks is related to each other in the rock cycle.

Water Cycle

Water constantly evaporates from the land surface, rivers, and the sea.
Sublimation is solid turning into a gas.
Water sublimes from ice and snow.
As water vapor rises it condenses into droplets.
Clouds are formed from condensed water droplets.
The droplets in clouds often freeze.
When droplets in clouds are heavy, they fall back to earth as precipitation.
Precipitation is hail, rain, sleet, and snow.
Water that falls over the sea goes back into the sea.
Water that falls over land goes into rivers or groundwater and makes its way back to the sea.
This cycle is called the water cycle.
The water cycle provides fresh water for animals and plants on land.
Plants take water from the ground and move it to their leaves where it evaporates into the atmosphere; this is transpiration.
Animals and plants produce water through respiration.
Animals excrete water in urine, feces, and sweat.
Animals and plants decay when they die, which releases water.

Carbon Cycle

Respiration in the cells of living things produces water and carbon dioxide from glucose and oxygen.
The carbon cycle is important for the survival of living organisms.
In the carbon cycle, carbon dioxide is absorbed by plants for photosynthesis.
In the carbon cycle, carbon dioxide is released by animals and plants during respiration.
In the carbon cycle, carbon is transferred to consumers in the food chain.
The carbon cycle returns carbon from organisms to the atmosphere as carbon dioxide.
Microorganisms help to cycle materials through an ecosystem by returning carbon from dead organisms to the atmosphere as carbon dioxide.

Air Pollution

The combustion of fuels is a major source of atmospheric pollutants.
Most fuels, including coal, contain carbon and/or hydrogen and may also contain some sulfur.
The gases released into the atmosphere when a fuel is burned may include carbon dioxide, water vapor, carbon monoxide, sulfur dioxide, and oxides of nitrogen.
Solid particles and unburned hydrocarbons may also be released that form particulates in the atmosphere.
Sulfur dioxide and oxides of nitrogen cause respiratory problems in humans and cause acid rain.
Particulates cause global dimming and health problems for humans.

Atomic Structure

Atoms are very small and have a radius of about 1 \times 10^{-10} m
Atoms consist of a positively charged nucleus, containing protons and neutrons, surrounded by negatively charged electrons.
The radius of a nucleus is less than 1/10000 of the radius of an atom.
The mass of an atom is concentrated in the nucleus.
The electrons are arranged in energy levels, which are different distances from the nucleus.
The atomic number is the number of protons in an atom of the element.
All atoms of a particular element have the same number of protons in their nuclei.
Atoms of different elements have different numbers of protons.
The mass number of an element is the total number of protons and neutrons.
The relative charges of the subatomic particles are: protons (+), electrons (-), and neutrons (0).

Electronic Configuration

Electron arrangement may change with the absorption or emission of electromagnetic radiation.
Electrons in an atom occupy the lowest available energy level.
The electronic structure of an atom can be represented by numbers or a diagram.
Atoms have no overall electrical charge because the number of electrons is equal to the number of protons in the nucleus.
Elements that react to form positive ions are metals.
Elements that do not form positive ions are non-metals.
Atoms form positive ions if they lose one or more outer electrons.
Atoms form negative ions if they gain one or more outer electrons.

Isotopes

Isotopes are atoms of the same element that have different numbers of neutrons.
An element’s relative atomic mass is an average value that takes account of the abundance of different isotopes.

Atomic Theory

Before electrons were discovered, atoms were thought to be tiny spheres that could not be divided any further.
The plum pudding model was developed after the discovery of electrons, with the atom thought to be a ball of positive charge with negative electrons embedded throughout it.
The nuclear model was developed after the alpha particle scattering experiment concluded that the mass of an atom was concentrated in the center (nucleus) and that the nucleus was charged.
Niels Bohr used theoretical calculations and experimental observations to adapt the nuclear model by suggesting that electrons orbit the nucleus at specific distances.
Protons were discovered after later experiments concluded that positive charges of any nucleus could be subdivided into a whole number of smaller particles, each with the same amount of charge.
Experiments by Chadwick provided evidence for the existence of neutrons within the nucleus, about 20 years after the nucleus became an accepted scientific theory.

The Periodic Table

Elements in the periodic table are arranged in order of increasing atomic number and elements with similar properties are in columns, known as groups.
It is called the Periodic Table because similar properties occur at regular intervals.
Elements in the same group have similar properties because they have the same number of electrons in their outer shell.
Early periodic tables had elements missing and some elements were placed in the wrong groups because the strict order of atomic mass was followed.
Mendeleev left gaps for elements he thought had not yet been discovered and changed the order of some elements.
Elements with properties predicted by Mendeleev were discovered and filled the gaps.
Knowledge of isotopes helped to explain why the strict order of atomic weights is not always correct.

The Noble Gases

Elements in Group 0 are called the Noble Gases.
They are unreactive and do not easily form molecules because they have a stable arrangement of electrons.
They have 8 electrons in their outer shell, except Helium which has 2.
Boiling point increases with increasing atomic mass (as you go down the group).

The Alkali Metals

Elements in Group 1 are called Alkali metals.
They have 1 electron in their outer shell.
They are soft and shiny and have relatively low melting and boiling points.
Reactivity increases as you go down the group.
Alkali metals react with oxygen to form metal oxides.
Alkali metals react with water to form metal hydroxides and hydrogen gas.
Chemical reactions can be represented by word equations or equations using symbols and formulae e.g. Sodium Hydroxide + Hydrochloric Acid à Sodium Chloride + Water
NaOH + HCl \rightarrow NaCl + H_2O
Elements in Group 7 are known as the Halogens.
They have similar reactions because they all have 7 electrons in their outer shell.
The Halogens are non-metals and consist of molecules made up of pairs of atoms.
Melting and boiling points increase with increasing relative molecular mass (as you go down the group).
Reactivity decreases as you do down the group.
A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.

The Transition Metals

Halogens
Metals including Cr, Mn, Fe, Co, Ni, and Cu are transition metals with similar properties, which are different from the properties of Group 1.
Many transition elements form ions with different charges, form colored compounds, and can be useful as catalysts.

Chemical Reactions

Chemical reactions always involve the formation of one or more new substances.
Chemical reactions often involve a temperature change.
Formulae are used to show the elements bonded together in a compound e.g. H2O contains 2 hydrogen atoms and one oxygen atom.
Compounds can only be separated into their elements by a chemical reaction. e.g. 2H2O \rightarrow 2H2 + O_2
In chemical equations the three states of matter are shown as:
- solid = (s); liquid = (l) and gas = (g)
- aqueous solutions are shown as (aq)
- e.g. 2Na(s) + 2H2O(l) \rightarrow 2NaOH(aq) + H2(g)
An aqueous solution is a substance dissolved in water.

Relative Formula Mass

The relative atomic mass (Ar) is the average mass of the atoms of an element compared to the mass of carbon-12.
The relative formula mass (Mr) of a substance is the sum of the Ar of all the atoms in the formula. e.g. What is the Mr of water (H2O)? Ar \, H = 1.0; O = 16.0
- There are 2 \times H and 1 \times O in the formula
- (2 \times 1.0) + (1 \times 16.0) = 18.0
Ar and Mr have no units as they are relative masses.
In a balanced chemical equation:
- sum Mr reactants = sum Mr products
- e.g. 2H2O2 \rightarrow 2H2O + O2
- Mr reactants = 2 34 = 68
- Mr products = (2 \times 18) + 32 = 68
The percentage mass of an element in a compound can be calculated using the relative atomic mass and the relative formula mass.

Conservation of Mass and Balancing Equations

No atoms are lost or made during a chemical reaction.
mass of products = mass of reactants
Chemical reactions can be represented by symbol equations which are balanced.
This means the number of atoms of each element is balanced e.g.
2Mg + O_2 \rightarrow 2MgO
- 2 magnesium \, atoms \, on \, each \, side
Some reactions may appear to involve a change in mass, but this is normally because a reactant or product is a gas e.g.

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

*   During the reaction hydrogen gas is produced. If the gas is free to leave the reaction container then the measured mass will decrease.

Uncertainty

Scientific uncertainty means there is a range of possible values within which the true value of a measurement lies.
Whenever a measurement is made, there is always some uncertainty about the result obtained.

Concentration

Many chemical reactions take place in solutions.
The more concentrated a solution the more particles it contains in a given volume.
The concentration of a solution can be measured in mass per given volume of solution e.g. grams per dm3 (g/dm3).
\frac{Mass \, of \, solute}{Volume \, of \, solution} = concentration
Volumes need to be in dm^3

Making Soluble Salts

Soluble substances dissolve in a solvent
Insoluble substances cannot dissolve in a solvent
Neutralization reaction general equation is acid + base → salt + water
Metal + acid → salt + hydrogen
Metal oxide + acid → salt + water
Metal hydroxide + acid → salt + water
Metal carbonate + acid → salt + water + carbon dioxide
Soluble salts can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides, or carbonates.
The solid is added to the acid until no more reacts and the excess solid I filtered off to produce a solution of the salt.
Salt solutions can be crystallized to produce solid salts.
Copper oxide reacts with sulfuric acid solution to produce copper sulfate and water CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l)
Copper sulfate solution