Science exam- year 9

Earthquake

The shaking of the Earth's surface caused by the sudden movement of tectonic plates.

Do earthquakes and volcanoes form in patterns?

Earthquakes and volcanoes form in lines and clusters. They can form along fault lines and places like the ring of fire. An area with lots of earthquakes and volcanoes is Indonesia running north to Japan.

Natural hazards

Events in the natural world that pose a danger to humans or other living things

- tsunamis

- volcanic eruptions

- earthquakes

Natural disasters

When natural hazards cause death and destruction

Tsunami

A large ocean wave caused by an earthquake or coastal landslide

Volcanic eruption

The release of hot liquid rock at the Earth's surface

Pressure + temperature in the Earth’s layers

As the depth below the earth’s surface increases, so does temperature and pressure

Crust

A layer of solid rock, 5-70 km thick, being thickest under the continents.

Mantle

The thickest of the four layers, made of mostly solid rock.

Outer core

Liquid mixture of iron and nickel, and its flow generates the earth's magnetic field.

Inner core

A solid mixture of iron and nickel at extreme pressures and temperatures (over 6000°C)

Pangaea

A supercontinent that existed 280 million years ago, which consisted of all of the continents

Continental drift theory

• In 1912, a German scientist called Alfred Wegener proposed a new theory, where continents once joined together as a supercontinent called Pangaea.

• Over millions of years, the continents slowly drifted into their present-day positions. He called this continental drift.

Evidence that supports the Continental drift theory

• The continents appear to fit together like puzzle pieces

• Fossils of land animals and plants of the same age have been found on different continents

• The same types of rocks and mountains line up between different continents

How can new evidence change a scientific theory?

• Scientific theories always aim to be the best explanation for the available evidence.

• Scientists often need to adapt their theories to account for new evidence. (seafloor spreading and Wegener's theory)

Smaller supercontinents

Pangaea was actually formed from two smaller supercontinents:

• Laurasia – present-day Asia, Europe and North America

• Gondwana – present-day Africa, South America, Antarctica, Australia and India

Seafloor spreading

When underwater volcanic eruptions create new igneous rock, new crust formed by these eruptions cause the seafloor to slowly spread apart

Tectonic plates

The rigid rock slabs that the earth’s surface is broken into.

Lithosphere

• The crust and the solid upper layer of the mantle. (Which is what makes up tectonic plates)

• The lithosphere sits on a layer of the mantle that is partially melted. This semi-liquid layer allows the plates to move horizontally, carrying the continents with them.

Plate boundary

The border between two tectonic plates

Convergent plate boundary

• Plates moving towards one another

• Earthquakes and volcanoes

(Convergent boundary)Oceanic–oceanic

• When two plates with oceanic crust collide, one plate sinks beneath the other into the mantle.

• This is called subduction. It produces a deep valley on the seafloor called an ocean trench.

• A chain of volcanoes forms as the subducting plate melts to produce magma.

(Convergent boundary)Oceanic–continental

• Subduction also occurs in this case.

• The much denser oceanic crust always sinks beneath the continental crust. 

• This produces a trench along the subduction zone and volcanoes on the continental crust.

(Convergent boundary)Continental–continental

• Continental crust is too light to sink into the mantle.

• So when two continents collide, the crust is pushed up to form high mountain ranges.

Divergent plate boundary

• Plates moving away from one another

• Earthquakes and volcanoes

(Divergent boundary)Oceanic–oceanic

• When two plates with oceanic crust pull apart, a mid-ocean ridge forms.

• Cracks in the thin crust allow magma to rise from the mantle.

• Eruptions from deep-sea volcanoes produce new oceanic crust.

• This causes slow seafloor spreading.

(Divergent boundary)Continental–continental

• A divergent plate boundary in the continental crust creates a long depression.

• This is known as a rift valley.

• Magma rises through the thinned continental crust and creates volcanoes.

Transform plate boundary

• Plates sliding past one another 

• Can be any combination of oceanic and continental plates: results are similar

• The two plates slide past each other along a large fault.

• Faults are not perfectly straight, so the movement of the plates causes pressure to build up at sticking points.

• When the pressure becomes too great, a sudden movement occurs and this triggers an earthquake.

• These faults do not usually allow magma to rise through the crust, so volcanoes are unlikely.

Oceanic crust 

Usually about 5–10 km thick and is mostly made up of basalt, a dense volcanic rock

Continental crust 

Usually between 20–70 km thick and is lighter than oceanic crust

Hotspot

• regions of the upper mantle that are hotter than usual.

• Magma rises from deep within the Earth to the surface

• This allows them to melt surrounding rocks to produce magma.

How hotspots form volcanic island chains

1. A hotspot in the mantle creates magma that forms a volcano

2. A second volcano forms above the hotspot and the first becomes inactive

3. Older volcanoes are eroded by rain, wind and landslides

4. A chain of volcanoes forms as the plate moves over the hotspot

Gravity

An attractive force between objects that have mass.

Orbit

The path taken by one object around another because of gravity.

satellite

any object in space that orbits around a larger body; such as the Moon or a space station that orbits Earth

terrestrial planet

a planet that is mainly composed of rocks or metals and has a solid surface

• orbits a star

• reflects light

gas planet

a planet that is mainly composed of gases

• orbits a star

• reflects light

galaxy

a cluster of stars, dust and gas held together by gravity, such as the Milky Way

A star

A giant gas ball that produces heat and light and is held together by gravity.

A moon

A natural satellite that must orbit another planet.
Our moon does not produce its own light, but instead reflects others light.

Our cosmic adress

Earth

solar system

milky way

local group

Virgo supercluster

the observable universe.

The sun

The star that we are locked in orbit around

Chemical reaction

In a chemical reaction, the bonds between atoms are re-arranged. This only involves an atoms electrons, the nucleus doesn't change.

Nuclear reaction

• A reaction in which an atoms nucleus changes by gaining or losing protons and neutrons.

• The element can change because the atomic number changes.

Nuclear fusion

• A type of nuclear reaction in which two atomic nuclei fuse together.

• Produces heat and light within the Sun

How the sun was formed

• Hydrogen gas in its core was exposed to extreme temperature and pressure.

• The atoms broke down into plasma- freely moving protons and electrons.

• The extreme conditions were ideal for nuclear fusion

• As the protons fuse together, they release photons- tiny packets of heat and light.

How stars are formed

1. A star forms in a giant cloud of dust and gas, called a nebula.

2. Hydrogen gas is pulled into a dense ball by gravity. Before it begins producing heat and light, this ball of gas is known as a protostar.

3. As the matter is compressed into smaller spaces, the temperature increases

4. Over hundreds of thousands of years, the cloud gets thicker and forms a giant spinning disc.

5. At the centre of the disc, gravity crushes the ball into a superdense, superhot ball.

6. Huge jets of gas burst out from the centre.

7. Over the next half million years the young star gets smaller, brighter and hotter.

Main sequence stars

1. The compression of hydrogen in a protostar continues for hundreds of thousands of years.

2. When the temperature reaches 13 million degrees Celsius, nuclear fusion begins.

3. This converts hydrogen into the next heavier element, helium.

4. Fusion releases massive amounts of energy as heat and light, so the star ignites- stars in this stable state are called main sequence stars.

5. The explosive outward force of fusion is balanced by the inward pull of gravity.

6. The two forces can balance each other for billions of years.

Small star

A star with less than 8 times the mass of the Sun

Small star life cycle

1. Helium gets hot enough to fuse, creating carbon & oxygen. This makes the outer layers expand and the stable star becomes a Red Giant.
2. Outer layers of the star escape the gravity of the core and drift away, forming a planetary nebula.
3. All that remains is the core, which is made up of hot & dense carbon and oxygen. This core is known as a white dwarf.

Large star

A star with more than 8 times the mass of the Sun

Large star life cycle

1. Forms a Red Supergiant by fusing helium into carbon and oxygen, and then progressively heavier elements up to iron.

2. Red supergiants eject most of their mass in catastrophic explosions, known as supernovas.

3. Stars 8-20 times the mass of the sun leave behind a neutron star, the remains of the core of a large star, made up of densely packed neutrons.

4. Stars more than 20 times the mass of the sun leave behind a black hole, an object with gravity so strong that even light can't escape it!

Redshift

• The stretching of light waves emitted by objects( the atoms producing light) moving away from us

• The farther away a galaxy is, the more its light is redshifted, indicating it is moving away from us.

Key discoveries that provided evidence that the universe is expanding.

1. Vesto Slipher - The light from nearly all stars is redshifted. This means that the wavelengths are longer than we would expect. It suggests that the stars are all moving away from us.

2. Edwin Hubble- The further away a star or galaxy is, the more its light is redshifted and the faster it's moving away from us.

3. Albert Einstein- Space itself can expand and contract. The evidence indicates that the universe as a whole is expanding.

The big bang

13.8 billon years ago, everything was contained at a single point. The rapid expansion afterward is known as the Big Bang.

Big Bang timeline

0- Everything is compressed,
1 second - the universe expands rapidly and space begins to cool
370,000 years - hydrogen and helium atoms form
200 million years - first stars and galaxies form
6 billion years - stars, planets and galaxies form, collide, explode, collapse into black holes, etc.
9 billion years - our sun forms.

Element

A substance made up of only one type of atom.

Subatomic particles

• Protons (positively charged)

• Neutrons (neutral charge)

• Electrons (negative charge)

Mass of subatomic particles

Protons and neutrons 1, electrons 1/1840

Most of an atoms volume is:

Empty space, while most of its mass is in the nucleus.

Parts of an atom

• Nucleus, protons, neutrons, electrons, empty space
  - Electrons float around in the shells of the atom.

Atomic number

The number of protons found in the nucleus of one atom in each element. (hydrogen 1, helium 2, lithium 3, etc.)

Neutral atoms

• An atom is neutral when the number of protons equals the number of electrons so the charges balance out.

• They have a net charge of 0.

Ions

• When a neutral atom gains or loses electrons, the protons stay the same.
  - The result is a particle with a positive or negative charge which is called an ion.

Repulsion and attraction of ions

Like charges repel and opposite charges attract.

How are ions represented

• An ion is represented by the element symbol followed by the overall charge in superscript

• e.g. O-2 is an oxygen ion with charge -2(it has two more electrons that protons)

Types of ions

Positive:
- Positive ions form when a neutral atom loses electrons so it has more protons.
Negative:
- Negative ions form when a neutral atom gains electrons so it has more electrons.

Static electricity

Electrons can transfer from one object to another through rubbing the objects together. This creates a charge imbalance known as static electricity.

Mass number

Mass number = the total number of protons and neutrons in the nucleus of an atom.

Isotopes

Atoms of the same element with different mass numbers. Isotopes are identified by their mass number, e.g.
Carbon -12, carbon -13 (stable), carbon -14 (unstable).

Stable isotope

The balance of protons and neutrons makes the nucleus unlikely to break apart.

Unstable isotope

The balance of protons and neutrons makes the nucleus likely to break apart.

Subatomic particle roles in elements

- When you add electrons to an atom, you change the net charge.
- When you add protons you change the element.
- When you add neutrons you change the mass number.
- Mass number - atomic number = number of neutrons.

Radioactive decay

- Having the wrong balance of protons and neutrons makes the nucleus unstable- too much mass or energy.
-Unstable atoms release energy or particles, known as radiation, in a process called radioactive decay.
-Releasing radiation stabilises the nucleus more.

Alpha radiation

Reason for decay: Too many particles in the nucleus
Description: An alpha particle made up of two protons and two neutrons bound together.
-Used in smoke detectors.
Atomic number -2
Mass number -4

Beta radiation

Reason for decay: Too many neutrons compared to protons in the nucleus.
Description: A neutron changes into a proton and shoots out a beta particle, which is a high-energy electron.
- Used to treat cancer
Atomic number +1

Gamma radiation

Reason for decay: Too much energy in the nucleus
Description: Energy leaves the nucleus as high-energy electromagnetic waves, known as gamma rays.
-Used to kill bacteria/ sterilise food.

Periods

The rows across in the periodic table

Groups

The columns down on the periodic table. Elements in the same groups have similar properties

Metals

Metals are on the left and middle side of the periodic table

Metalloids

Metalloids can be found on either side of the staircase line between nonmetals and metals (centre right). They are a combination of the properties of metals and nonmetals.

Nonmetals

They are found on the upper right side of the periodic table. They are bad conductors of heat and electricity and are mostly dull.

Electron Configurations.

Electrons are confined to shells. The arrangement of electrons in the shells.
1st shell - 2 electrons
2nd shell - 8 electrons
3rd shell - 8 electrons
4th shell - 2 electrons.

Electron shells

Rings around the nucleus in which electrons are stored. To write the electron configuration, write the number of electrons in each shell with a point in between, e.g. 2.8.7.

Valence shells

The outermost occupied shell of an atom.

Valence electrons

- The electrons located in the valence shell.
- The number of valence electrons determines how atoms will interact.
- The period in which an element is located relates to the number of shells that contain electrons.
-The group in which an element is located relates to the number of valence electrons.

Reactivity

• A substance's tendency to chemically interact with other substances
  - Fluorine (F) and caesium (Cs) are widely regarded as the most reactive elements on the periodic table.

Groups 1 and 2 reactivity

These are highly reactive metals because they only need to lose one or two electrons to be stable.

Groups 16 and 17 reactivity

These are highly reactive non-metals because they only need to gain one or two electrons to be stable.

Why do atoms lose, gain or share electrons in a chemical reaction.

To achieve a full valence shell, so that they can be stable.

Atomic radius

The distance from the nucleus to the valence shell.

How does the atomic radius determine the reactivity of elements (for metals)?

- The larger the atomic radius the more reactive the element is.
- This is because a larger atomic radius means the valence electron is farther from the nucleus and less tightly held, making it easier to lose, increasing reactivity.

How does the atomic radius determine the reactivity of elements (for non- metals)?

- The smaller the atomic radius the more reactive the element is.
-This is because the valence electrons are closer to the nucleus, making it easier to attract additional electrons to fill the valence shell, thus increasing reactivity.