Bonding and Chemical Reactions

Law of Conservation of Mass

• the law of conservation of mass states that in a chemical reaction mass is neither created nor destroyed

• this is why chemical equations must be balanced

• the amount of atoms on the left hand side (the reactants) must be equal to the amount of atoms on the right hand side (the products)

Endothermic and Exothermic reactions

Energy in a Reaction

• when a chemical reaction occurs, 2 things happen

  • bonds are formed

  • bonds are broken

Energy requirements

• reactions are very rarely spontaneous

• they require initial energy to start

• bringing a flame to the bunsen burner allows the gas to ignite and the combustion reaction to begin

• the minimum energy required for a reaction to begin is called the activation energy

• once the activation energy has been reached, the reactants have enough energy to collide with each other and form products

Releasing or absorbing?

• if the reactants absorb more energy from the products release, then the reaction overall absorbs energy - an endothermic reaction

• if the reactants absorb less energy than the products release, then the reaction overall releases energy - an exothermic reactants

Combustion

the rapid chemical combination of a substance with oxygen, involving the production of heat and light

Products of combustion

• when fuels (hydrocarbons) react with an excess supply of oxygen - they will react and produce water vapour and carbon dioxide

• this is an example of complete combustion

• eg. methane + oxygen → water + carbon dioxide

• complete combustion occurs when there is a plentiful supply of oxygen - like the heating flame of a bunsen burner

• incomplete combustion occurs when there is limited oxygen and other products like carbon monoxide and soot can form - like the safety flame of a bunsen burner

Rates of Chemical Reactions

Fast and slow chemical reactions

• the rate of reaction is described as the speed at which a chemical reaction takes place

• eg. some reactions are slow, such as rusting, and some are fast, such as burning

• the rate of reaction can be found by measuring the amount of reactant used up, or the amount of product formed, in a given time

Collision theory

• for a chemical reaction to occur, the reactant particles must collide

• but collisions with too little energy do not produce a reaction

Successful reactions occur when:

• the particles have enough (activation) energy

• the rate of reaction depends on the rate of successful collisions between reactant particles

• the more successful collisions there are, the faster the rate of reaction

Factors that affect rate of reaction

Changing temperature

if the temperature is increased:

• the reactant particles move more quickly

• they have more energy

• the particles collide more often, and more of the collisions result in a reaction

• the rate of reaction increases

Renewable energy and electricity

Charging by friction

Current

a continuous loop of electrons flowing through a circuit. a circuit requires a

• power source eg a battery

• conducting material eg wires/leads

• load eg a light bulb, phone, laptop, air conditioner

Magnetism

• magnetism is one of the most important forces in the universe

• a non-contact, or a field force, that attracts or repels

Electromagnetism

the interaction between electric currents and magnetic fields is called electromagnetism. It involves two main relationships:

• electric currents produce magnetic fields

• like poles repel, opposites attract

• changing magnetic fields can produce electric currents

How do we use magnets to make electricity?

• a magnet can produce an electric current in a wire when it is moving

• this is called induction

• changing the magnetic field can ‘induce’ a current in a wire

Magnetic field on an electric current

• an electric current flowing through a wire creates a magnetic field around it

• so the wire acts as a magnet whenever it is ‘switched on’ by electricity

• this type of temporary magnet is called an electromagnet

Generators

• whenever you have a moving magnet surrounded by wires, or wires moving through a magnetic field, you will create electricity

• we take advantage of this when we generate electricity

• as the magnet is spun, its magnetic field moves around the circle and the magnetic field lines ‘cut’ the wires

• this change in magnetic field then causes electricity to flow in the wires

• mechanical energy can be converted into electrical energy using a turbine

force such as

• moving water

• pressurised steam

• forceful wind

→ spins turbine → spins shaft → spins generator - magnets spinning past wire coils generate electricity → electrical output - travels through the network system to → your homes - schools and local businesses in your community

Calculating Resistance in a circuit

for a series circuit:

Rseries = R1 + R2 + … + Rn

where Rseries is the equivalent effective series resistance and R1, R2… Rn are the individual resistances

for a parallel circuit:

1/Rparallel = 1/R1 + 1/R2 + 1/Rn

where Rparallel is the equivalent effective resistance and R1, R2…Rn are the individual resistances

for a mixed circuit:

calculate the equivalent parallel component and add the series resistor

Ohm’s Law

• when we connect wires to a battery to complete a circuit, even the best conducting wires restric the amount of current that can travel

• Georg Ohm established the result that:
  

• Ohm found that the current produced by a 6V battery = 2 × 3V battery

• resistance is described as the ratio of potential difference across a component to the current through the component

R = V/I

V=IR (omega symbol) Ohms

• Ohm’s Law is true for metals, but not for most other materials

Ohmic versus non ohmic

• conductors that obey Ohm’s law are known as ohmic conductors

• ohmic conductors are usually called resistors

• an ohmic conductor can be identified by measuring the current that flows through the conductor when different potential differences are applied across it

Inheritance and Evolution

Traits

Variation within species

• members of the same species show variation in their traits or characteristics

• how many traits canyou think of that show variation in humans?

• what causes these unique traits/characteristics in an individual?

Causes of variation

• people are different because they inherit different characteristics from their parents

• for humans especially but for all species, the environment can also have a significant effect on traits/characteristics

• the unique characteristics of an individual are caused by:

  • the unique set of genes they have received from their parents (50% from mum, 50% from dad)

  • the environment in which they have developed

• differences in certain characteristics are due to a combination of inherited and environmental factors

Reproduction

Asexual vs sexual reproduction

Asexual

• there is no union of gametes (sex cells - egg and sperm for humans and other mammals, ovules and pollen for plants)

• offspring come from one parent organism only

• offspring are mostly genetically identical to parents (mutation can lead to genetic differences)

• occurs in bacteria, some plants and a few animals

Sexual

• there is the union of gametes to combine genetic information of two parents - known as fertilisation

• offspring come from two parents

• offspring show a great deal of genetic diversity because of the combination of genes from parents

• occurs in most plants and animals

Mitosis and Meiosis

Mitosis vs meiosis

Mitosis

• simple cell division in body cells

• involves the replication of all of the DNA in the cell, followed by the splitting of the DNA between two cells

• original cells are called parent cells, and the newly formed cells are called daughter cells

• daughter cells are identical to parent cells in number of chromosomes and genetic information

Meiosis

• cell division in the sex cells (egg and sperm)

• involves the replication of all of the DNA in the cell, followed by the splitting of the DNA between two cells, each of which splits again (results in 4 cells total)

• daughter cells are non-identical to parent cells in number of chromosomes (23 in humans) and genetic information

Gregor Mendel: The History of Genetics

Definitions

Gene

a specific sequence of nucleotides found on a chromosome, which codes for a specific trait/characteristic in a living thing

Allele

the different versions of a gene

Dominant

the allele that will be expressed if it is present in an individual

Recessive

the allele that will be covered up by the dominant allele if both are present, and will only be expressed if both alleles are recessive

Who was Gregor Mendel?

• Gregor Mendel was an Austrian monk

• he lived in a monastery in what is the Czech Republic today

• having lots of time on his hands and lots of land, as well as access to greenhouses, Mendel embarked on extensive experimentation on pea plants, to try and figure out how traits were inherited from parent plant to offspring plant

• his research occurred in the mid 1800s - 150 years before modern scientists discovered the structure of DNA, and before we understood what DNA was

• despite having no access to technology, no access to the biological sciences, and no knowledge or understanding of DNA, Mendel was able to describe inheritance patterns in great detail, and is now known as the father of modern genetics

What did Mendel find?

• Mendel’s first discovery was that offspring plants did not always look like parent plants. two tall pea plants crossed together would not always give rise to tall pea plants

• he also discovered that with the traits he was observing, plants either had one trait or the other, not a mixture

• finally he found that when he bred great numbers of offspring plants, the outcomes of the appearance of traits would have a pattern - he began to predict these patterns and his crosses would almost always lead tot the expected results

What were Mendel’s conclusions?

• for every trait he studied, there was a dominant and a recessive version of the trait (we now know these as alleles)

• offspring plants receive a copy of the inheritance factor (we now know these as genes) from each parent - they can be the same version, or different versions

• therefore, every offspring plant carries two copies of each inheritance factor, and the characteristic they display is based on the combination of factors they possess

• if an offspring plant receives 2 dominant inheritance factors, one from each parent, they will display the dominant characteristic

• if an offspring plant receives 2 recessive inheritance factors, one from each parent, they will display the recessive characteristic

• if an offspring plant receives 1 dominant and 1 recessive inheritance factor, they will display the dominant characteristic

Example of Mendel’s experiments

• Mendel began every experiment with pure breeding parent plants - in this case, a tall plant and a short plant which carry only the alleles for that characteristic

• then, he took the offspring plants from that first cross and bred them with each other

• with this second cross, he reliably found that the offspring plants followed a 3:! ratio of the dominant characteristic to the recessive characteristic

• he concluded that the two plants from the F1 generation must have had a tall and a short allele each - so when the gametes with these alleles fused during fertilisation, it lead to 3 possibilities for the offspring

Mendel’s contribution

• Mendel’s breakthrough was that he recognised a pattern in the inheritance of characteristics by offspring from their parents and so he was able to propose a model of inheritance

• using mathematical calculations and huge amounts of repetition, he was able to predict the ratios of various types of offspring from any two specific parents

• he was an impeccable record keeper - though his work wasn’t appreciated when he did it, his notebooks and records have allowed current scientists to confirm how significant his work was

Genes and Alleles

Chromosomes, genes, alleles and variations

• each chromosome passed along from each parent contains the genes for many traits, for example eye colour, hair colour, haemophilia etc

• therefore offspring receive 2 copies of every gene - one from their mother and one from their father

• each version of a specific gene is known as an allele

• for most genes, there will be a dominant allele and a recessive allele

Definitions

Genotype

the combination of two alleles in which an individual has for a specific trait (ie BB, Bb or bb)

• homozygous - both alleles of the genotype are the same

• heterozygous - the alleles of the genotype are different

Phenotype

the observable characteristic expressed in an individual, as controlled by the individual’s genotype

with a homozygous dominant or heterozygous genotype, the dominant trait will be expressed

with a homozygous recessive genotype, the recessive trait will be expressed

Eyes and eye colour

• eye colour tends to be used to teach genetics as it’s something we can all relate to as humans

• it is highly simplified to teach high school genetics - we know there are more thn just brown and blue eyes, but we pretend for the sake of simplicity

Evolution and Natural Selection

Evolution

• the process by which different kinds of living organism are believed to have developed from earlier forms during the history of the earth

Jean Baptiste Lamarck

• one of the first scientists to try and explain how evolution works

• he stated that giraffes had become long necked because they had stretched to reach the leaves high up, this elongated their neck and their offspring were born with longer necks

• scientists tested this theory by cutting off rats tails and observing that their babies still had tails

Charles Darwin

• Darwin made several observations about evolution but his most famous theory is ‘natural selection’

• by observing finches in the Galapagos he noticed that the finches with different beak types lived in areas where the environment favoured their beak

• these observations led him to propose the currently most accepted theory of evolution

• what he called ‘characteristics’ we now call genes

Natural Selection

• within every species there is natural variation of characteristics

• organisms with favourable characteristics suited to their environment will survive longer and live to reproduce

• these favourable characteristics are passed down to the offspring, and over several generations this trait becomes more common in the population

• organisms with unfavourable characteristics will often die before reproducing, slowing the spread of the unfavourable trait

• given enough time all organisms will show the favourable trait and the unfavourable trait will be bred out

• if the environmental change is too drastic, an extinction may occur

Variation

Species

a group of organisms that can interbreed and produce fertile offspring

Variation

differences between individuals within a species

Why is variation important?

• if environmental conditions stayed perfectly constant at all times, variation would not be necessary

• if environmental conditions are changing, variation within a species means that some will survive and some will not survive adverse condition - this is the basis of natural selection and evolution

How is variation produced?

1. mutation in the sex cells

   if a mutation occurs in a body cell, it will not be passed on to the next generation

2. during meiosis, there is a crossing over of information between homologous chromosomes

3. independent assortment (seperation of pairs) of chromosomes and random segregation of chromatids during meiosis

4. random fertilisation

Natural selection mnemonic device

• to survive in a particular environment, organisms must possess traits that favour their survival in that environment

• populations of organisms possess natural/coincidental variations that can become adaptations to an environment

• natural selection occurs if the following criteria are met:

  • variation - there is a random variety of traits within a population

  • inheritance - traits can be inherited

  • selection - some traits allow an organism to survive, and some do not

  • time - many generations are required before change can be observed, and many offspring die in the process (so the species must ‘over-reproduce’)

  • adaptation - the species becomes better adapted to its environment

Two types of evolution

Divergent evolution

when differences are apparent in closely related species, this is indicative of recent divergence from a common ancestor

Convergent evolution

when similarities appear in distantly related or apparently unrelated species, this is indicative that the pressures of the similar environments these species live in have resulted in them adapting to their environments through evolution

Evidence for Evolution

Defining a species

• closely related species share many genetic traits

• careful observations of these traits can provide evidence that two species are closely related

• but how do we know that they are distinct species at all?

• any group of organisms that can breed to produce fertile offspring is called a species

• this ability to reproduce allows a species to continue to exist and evolve

How do new species form?

• the formation of a new species is called speciation

• this process is explained by the theory of evolution by natural selection

Step 1: isolation of a population

Step 2: evolution under different selection pressures

Result: distinct species

Extinction

• extinctions occur when there are no remaining individuals of a species still alive

• species that are poorly adapted to their environment are less likely to survive and reproduce compared to species that are well adapted to their environment

• if they are unable to survive and reproduce sufficiently to maintain their population numbers they will eventually go extinct

• some factors which may contribute to the extinction of a species include:

Global Systems

Global Sph eres

• all habitats on earth are located in what could be considered a life-support zone

• this thin layer of our planet includes the atmosphere, the ocean depths, and the upper part of the Earth’s crust and its sediments

Biosphere

• the biosphere is the life-support system of our planet

• it consists of the atmosphere, lithosphere, hydrosphere and biota (living things), the interactions between them, and the radiant energy of the sun

• the biosphere includes all of the ecosystems on earth

• interactions within the biosphere includes all of the ecosystems on earth

• interactions within the biosphere include the cyclical movement of essential elements such as carbon, nitrogen and phosphorus

Atmosphere

• the earth’s atmosphere is divided into the troposphere (lower atmosphere) and the stratosphere (upper atmosphere)

• the troposphere is around 6-17 kilometres depending on your latitude

• the stratosphere is about 50 kilometres thick and contains an area known as the ozone layer

• while this layer allows visible and infra-red radiation from the sun through, it absorbs ultraviolet radiation

• this reduces the amount of damaging UV radiation reaching earth’s surface

Human activity and the atmosphere

• chlorofluorocarbons (CFCs) have been used as coolant agents in refrigerators and air conditioners, as propellants in aerosols, and as industrial solvents

• their use has resulted in an increased amount of those compounds being released into the atmosphere

• once in the stratosphere they are broken down into chlorine atoms, which destroy ozone molecules

• this has led to depletion of areas of the ozone layer, increasing the amount of damaging UV rays that get through and causing damage to living organisms

Human activity and the hydrosphere

• toxic or industrial wastes and untreated sewage in water systems have made their way into rivers, bays and the ocean, which has had a direct impact on the hydrosphere

• toxins can move along food chains, in some cases being biologically magnified - getting more concentrated - as they move up the chain

• while some of these wastes are purposefully dumped, in other cases they enter the water system in run-off from the land or are washed out of the atmosphere in rain

Lithosphere

• the earth’s soil and rocky crust, along with the uppermost section of the mantle on which they sit, make up the lithosphere

• it is within this sphere that igneous, sedimentary and metamorphic rocks are formed, broken down and changed from one type to another

Human activity and the lithosphere

• overstocking, soil exhaustion, salinity, pesticides, unstable landfill, salinisation, toxic seepage, excessive clearing, chemical emissions, deforestation and soil erosion can all be very destructive to the lithosphere

• overgrazing and deforestation may also result in desertification

• they can have detrimental effects on habitats and resources and hence the survival of organisms within the ecosystem that they are affecting

The Carbon Cycle

Why is carbon important?

• carbon is the main constituent of all living cells (biochemistry, organic chemistry)

• carbon can form long chained-molecules which are the basis for fats, carbohydrates, nucleic acids (DNA and RNA) and proteins

• component of fuel (coal and gas)

• used in nanotubes for computers

Common reactions using carbon

Respiration

glucose + oxygen → carbon dioxide + water + energy

Photosynthesis

carbon dioxide + water + light energy → glucose + oxygen

Combustion

burning of fuel to release carbon dioxide

The Nitrogen Cycle

Why is the nitrogen cycle important?

• nitrogen is an element that is essential to build proteins

• ~78% of air is nitrogen gas (N_2)

• bacteria break down nitrogen that has entered the soil

• plants absorb nitrogen from the ground and animals eat plants and other animals

• decomposing animals and plants return nitrogen to the soil