Science (Semester 1) Flashcards
What are atoms made up of?
Matter
Draw a diagram of an atom.
CARBON ATOM: 6 protons + 6 neutrons in nucleus 6 electrons spread across two rings 2 in first ring 4 in second
What is a scientific theory?
a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed through observation and experimentation
How can theories be revised?
Theories are revised gradually as scientists find improvements to the theory and ‘build’ upon it.
How can theories be disproved?
Theories can be disproved by experimental results contrary to a theory’s predictions.
Discuss the atomic theory proposed by Dalton.
Dalton’s atomic theory was based on experimentation and first-hand examination. This made his theory the first scientific theory.
Summarise Dalton’s atomic theory of matter
- All matter is composed of atoms, which are indivisible and indestructible
- All atoms of an element are identical, but different elements have atoms of differing size and mass
- All compounds are formed by combinations of atoms in defined ratios.
- Chemical reactions result in the rearrangement of atoms in the reactant and product compounds
Recall some of the early models of the atom.
- Democritus’s atomic theory
- Dalton’s atomic theory of matter
- Thomson’s plum pudding model
- Rutherford model
Discuss Thomson’s Plum Pudding model of the atom.
- Atom composed of electrons
- Electrons surrounded by a ‘soup’ of positive charge to balance electron’s negative charge
- Electron arranged in rotating rings
Describe Rutherford’s gold foil experiment.
- Alpha particles with large kineticenergies were shot towards a thin foil of gold
- A ‘ring’ detector was set up around the gold foil to detect the alpha particles and where they scattered
- Most of the alpha particles passed through, but others were deflected at small angles or REFLECTED BACK AT THE SOURCE.
- This indicated a strong central positive charge.
Describe the gold foil experiment’s implications for the structure of the atom.
- Disproved Plum Pudding model
- Revealed that atom was mostly empty space
- Strong central positive charge in nucleus, which has majority of mass
- Electrons moved around in space around nucleus
- Thus, new planetary model was developed.
Discuss Rutherford’s gold foil experimental setup.
- A radioactive source rich in positively charged heavy alpha particles was inside a cube shaped thick lead box with a narrow opening
- The narrow opening confined the alpha particles into a beam
- A thin gold foil was set up away from the radioactive source (which would be bombarded by the alpha particles)
- A circular florescent detector was set up around the gold foil - screen coated with zinc sulphide flashed when alpha particles hit it
How were the results of the gold foil experiment interpreted?
- Most of the alpha particles passed through the foil undeflected: Atom mostly empty space
- Some alpha particles deflect by small angles: Strong positive charge in nucleus
- Small fraction of alpha particles reflected back: Nucleus has most of mass
Why did Rutherford propose the existence of neutrons?
- Atomic number of atom usually above half its atomic mass
- However, nuclei with 2x charge had at least double the mass that was expected from the protons contained (DISPARITY)
Why was it difficult for Rutherford to prove the existence of neutrons?
Neutrons hold no charge, thus they could not be detected by electric/magnetic fields.
What charge does a proton hold?
Positive
What charge does an electron hold?
Negative
What charge does a neutron hold?
None
Calculate the numbers of protons, neutrons and electrons in an atom given its mass and atomic numbers.
Atomic number = no. of protons = no. of electrons
Mass number = no. of protons + no. of neutrons
Neutrons = atomic number - mass number
Explain the relative atomic mass scale.
weighted average of masses of isotopes in a naturally occurring element relative to mass of carbon-12 atom (standard)
How are atomic numbers determined?
Atomic number = no. of protons = no. of electrons
How are mass numbers determined?
Mass number = no. of protons + no. of neutrons
What are isotopes?
different forms of an atom that vary in mass and number of neutrons
How are isotopes similar and different?
- Isotopes (of the same element) share similar physical/chemical properties
- Isotopes differ in their number of neutrons and thus atomic mass
- Some isotopes are unstable, and will undergo radioactive decay to become another element.
How does the abundance of isotopes lead to the calculation of relative atomic mass?
- Most elements have more than one naturally occurring isotope
- Thus, the average mass of the isotopes of an element is used.
- Relative atomic mass is listed on the periodic table.
What are electron shells?
a grouping of electrons in an orbit surrounding the nucleus of an atom
- The more energy electrons have, the further their orbit. The closer, the most stable.
- The valence shell determines the element’s chemical / bonding properties
List the maximum number of electrons the four electron shells can hold.
First shell: 2
Second shell: 8
Third shell: 8 (up to calcium), 18 (above calcium)
Fourth shell: 32
Do you draw the electrons in pairs?
Yup.
What are the implications of flame tests?
- When atoms of an element are excited (flame) and electrons jump energy levels (and back), a photon is emitted (light) that releases a certain amount of energy of a particular wavelength
- The bigger the jump, the more energy released.
- The wavelength is represented by a coloured line in the emission spectrum.
- Each element has an unique spectrum, as the possible values of energy for the electrons present are different for each element.
- Thus, the flame test allows us to observe the colours emitted by an excited element, and thus distinguish between different elements.
Explain the colours in flame tests in terms of subatomic structure and relate colours to energy gap between electron shells.
- Electrons jump energy levels inside an atom when excited. The distance between the ground and excited state is called the energy gap.
- Photons with a high frequency (e.g. blue light) have a large energy gap.
- Photos with a low frequency (e.g. red light) have a low energy gap.
What colour do photons with a high frequency usually take on?
Blue light
What colour do photons with a low frequency usually take on?
Red light
What is alpha radiation?
- Alpha particles similar to helium nucleus (2 protons, 2 neutrons)
- Positive charge of +2
- Low penetration power due to large size
- Alpha decay occurs when radioisotope’s nucleus has excess protons
- Alpha particle emitted to keep neutron/proton balance
- Mass of 4 Daltons
What charge does alpha radiation hold?
+2
When does alpha decay occur?
When the nucleus of a radioisotope has excess protons, and an alpha particle is emitted to keep neutron/proton balance
What is the mass of an alpha particle?
4 Daltons
What is beta radiation?
- An electron
- Charge of -1
- Smaller mass gives it high penetration power
- Beta decay occurs when radioisotope has excess protons/neutrons
- Neutron decays into proton and electron - proton emitted, but electron kept, increasing atomic number by one, thus changing element
What charge does beta radiation hold?
-1
When does beta decay occur?
- Beta decay occurs when radioisotope has excess protons/neutrons
- Neutron decays into proton and electron - proton emitted, but electron kept, increasing atomic number by one, thus changing element
How is a beta particle produced?
When a neutron decays into a proton and electron, and the proton is emitted but electron kept
What is gamma radiation?
- A stream of high-frequency electromagnetic waves with NO MASS/CHARGE
- Highest penetration power - can penetrate most common substances
- Gamma decay occurs when radioisotope’s nucleus energy level is too high after emission of alpha/beta particle
- Gamma ray photon emitted in order to decay to lower energy state
When does gamma decay occur?
Gamma decay occurs when the energy level of a radioisotope’s nucleus, after the emission of an alpha/beta particle is too high.
A gamma ray photon is emitted in order to decay to a lower energy state.
What does the gamma ray photon release?
Electromagnetic radiation.
What is half-life?
the time taken for the radioactivity of a specified radioisotope to fall to half its original value
How can radiation be used in carbon dating?
- Carbon-14 is a radioisotope which appears in all living organisms.
- After an organism dies, it stops taking in carbon-14 and the carbon-14 contained at the time of death decays and thus the radioactivity of the material decreases.
- The approximate time since the organism died can be worked out by measuring the amount of carbon-14 left in its remains compared to the amount in living organisms.
How is radiation used in nuclear power?
Nuclear reactions are used in some countries as the source to generate some/most of their electricity.
How is radiation used in medicine?
Radioactive substances are used in research, diagnosis and treatment. Brachytherapy (radiation therapy inside the body) is used as a treatment for cancer.
Explain nuclear power.
Nuclear power relies on nuclear fission to make energy.
What is nuclear fission?
Nuclear fission happens when a neutron hits an uranium atom and splits it, releasing energy in the form of heat and radiation. This releases more neutrons, which hit more uranium atoms and the process repeats. This is called a nuclear chain reaction.
How does a nuclear power plant work?
- Nuclear energy is converted into heat in a nuclear reactor.
- The heat is transferred to water, turning it into steam.
- The steam drives a turbine, which drives electricity generators to convert the mechanical energy into electricity.
- The electricity flows out to a power grid.
Evaluate the dangers of radiation.
Radiation can damage the cells in your body by ionising atoms and changing the properties of them - free radicals are released in the process, which can damage DNA.
List the uses of radiation in medicine.
- Diagnosis
- X-rays, scans, injection of radioactive material for nuclear medicine imaging (tracers)
- Treatment
- Brachytherapy
- Placement of radioactive substance near tumour kills cancerous cells
- Radiation therapy
- External beam of radiation
- Swallowing, or injection of radioactive materials
- Brachytherapy
Understand the concept of the Big Bang theory.
- The universe started with a small singularity, then inflated to the current cosmos.
- In the first second after the universe began, a 10 billion degree cosmos existed that included neutrons, protons, electrons, anti-electrons, photons and neutrinos.
- As the Universe cooled, the neutrons decayed into protons and electrons, or combined with protons to make deuterium.
- Eventually, the Universe reached a temperature cool enough where free electrons combined with nuclei to create neutral atoms. This made the Universe transparent.
- It was opaque before, because the free electrons would have caused light (photons) to scatter.
What is the nuclear genesis theory?
the process that creates new atomic nuclei from pre-existing nucleons, primarily protons and neutrons
How is the periodic table organised?
- By atomic number
- Organised by periods (rows) and groups (columns)
- The period an element is in indicates the number of electron shells in it.
- The group an element is indicates the number of valence electrons.
- Periods are organised by weight, increasing from left to right and top to bottom
- Groups are organised by similar characteristics
What does the period an element is in indicate?
The number of electron shells in it
What does the group an element is in indicate?
The number of electrons in its valence shell.
How was the current periodic table developed?
Pre 1869, the periodic table was organised according to metals and non-metals, and chemical symbols were added - a system of atomic weights was also developed.
In 1869, Mendeleev organised the 63 elements into order of atomic weight and into groups with similar properties. From there on, noble gases were discovered by refrigeration, the elements were sorted by atomic number (using X-rays) and nuclear processes were used to identify nine transuranium elements.
What are the properties of metals?
- Lustrous (shiny)
- Can conduct heat and electricity
- Malleable (able to be shaped)
- Ductile (able to be drawn out into thin wire)
What are the properties of non-metals?
- Dull / not lustrous
- Poor conduction of heat / electricity
- Non-malleable (brittle)
- Non-ductile
Differentiate between metals and non-metals
Metals
- Lustrous (shiny) - Can conduct heat and electricity - Malleable (able to be shaped) - Ductile (able to be drawn out into thin wire)
Non-metals
- Dull / not lustrous - Poor conduction of heat / electricity - Non-malleable (brittle) - Non-ductile
Where are the alkali metals located in the periodic table?
Group 1
Where are the alkali earth metals located in the periodic table?
Group 2
Where are the transition metals located in the periodic table?
Groups 3-12
Where are the metalloids located in the periodic table?
Border stair-stepped line
Where are the halogens located in the periodic table?
Group 17
Where are the noble gases located in the periodic table?
Group 18
Recall the name, symbol, colour, features and uses of at least three common metals
Aluminium: Al, shiny/silver, low density/weight + super malleability + good thermal and electrical conductivity, used to make foil wrap and silver paper
Iron: Fe, silvery grey, easily malleable + durable + rusts easily, commonly used metal - magnetic
Gold: Au, shiny yellow, extremely malleable/ductile + good conductor of electricity/heat + dense, used in electronics and jewellery and as money
Copper: Cu, shiny brown, resistant to corrosion + anti-bacterial properties + super malleable + second greatest thermal/electrical conductivity, used in electrical wires and water pipes
What is the symbol for aluminium?
Al
What is the symbol for iron?
Fe
What is the symbol for Gold?
Au
What is the symbol for copper?
Cu
What are the features of aluminium?
Low density/weight
Superior malleability
Good thermal and electrical conductivity
What are the features of iron?
Easily malleable
Durable
Rusts easily
What are the features of gold?
Extremely malleable/ductile
Good conductor of electricity/heat
Dense
What are the features of copper?
Corrosion-resistant
Anti-bacterial properties
Super malleability
Second greatest thermal/electrical conductivity
What is aluminium used for?
Used to make foil wrap and silver paper
What is iron used for?
Commonly used metal - magnetic.
What is copper used for?
Used in electrical wires and water pipes
What is gold used for?
Used in electronics and jewellery and as money
Recall the name, symbol and special properties of at least two metalloids and their location on the periodic table.
Metalloids are located on the stepped border between metals and non-metals.
Boron / B / Good conductor at high temperatures + compounds used (e.g detergents)
Silicon / Si / Used as semiconductor + Brittle + Inactive at room temp
Arsenic / As / Tarnishes when in contact with air + Oxidizes when heated + Used to give color to flame in pyrotechnics
Recall the name, symbol and characteristic of at least two non-metals
Carbon / C / Highest melting point of all elements + can exist in several allotropes + has highest thermal conductivity in form of diamond + in form of graphite, one of softest substances
Fluorine / F / Most reactive element + Lightest halogen
+ Reacts violently with water to produce oxygen and hydrofluoric acid
Chlorine / Cl / Toxic gas that irritates skin, eyes and respiratory system + Sharp smell + Powerful bleaching, oxidising and disinfecting agent
Xenon / Xe / Colorless and odorless + Inert towards most chemicals