C3 - Atoms, elements and compounds Flashcards
Element
A pure substance made of only one kind of atom (e.g. He)
Atom
The basic unit of a chemical element (e.g. O2)
Compound
A substance made up of atoms of two or more different elements joined by chemical bonds (e.g. NH3 - ammonia)
Molecule
A group of atoms bonded together (can be of a single type of element, or of multiple types)
Mixture
A combination of two or more substances that are not chemically combined
Physical changes
A type of change that alters the physical properties of a substance but does not change its composition
- no movement of atoms
- change in form or appearance that can be undone
Chemical changes
Changes that alter the composition of matter
- movement of atoms
- formation of new substances that cannot be undone
Properties of chemical changes (name 3)
- gas produced (no addition of heat)
- change in composition
- change in temperature (without heat)
- cloudiness
- change of colour (without heat)
- formation of solid
Properties of physical changes (name 3)
- same composition
- change in temperature only when manually heated
- change in colour only when manually heater or cooled
- gas produced when heated manually to boiling point
- solid formed when frozen
Sublimation
solid to gas
Deposition
gas to solid
Boiling
liquid to gas
Condensation
gas to liquid
Melting
solid to liquid
Freezing
liquid to solid
Solvent
A liquid substance capable of dissolving other substances
- in which the solute dissolves
- in the highest proportion in solution
Solute
The substance that is dissolved within a solvent
- found in lower concentration in solution
Solution
A homogeneous mixture of two or more substances (solvent, solute)
Proton
A subatomic particle found within the nucleus of an atom
- CHARGE: positive
- RELATIVE ATOMIC MASS: 1
Electron
Subatomic particles distributed along the shells of an atom
- CHARGE: -1
- RELATIVE ATOMIC MASS: 0.0005 / 0
Neutron
A subatomic particle found in the nucleus of an atom
- CHARGE: neutral/0
- RELATIVE ATOMIC MASS: 1
Reading the periodic table (periods, groups, proton number, atomic mass)
Periods: show the number of shells of a single atom of that type of element
Groups: show the number of electrons on the outer shell of an atom of that element
- proton number/atomic number: the number of protons and the number of electrons (same amount)
- atomic mass: protons + neutrons
Isotopes
Atoms of the same element that have different numbers of neutrons
- with the same properties because they have the same number of electrons
Types of hydrogen isotopes
- protium (1P, 0N)
- used in hydrogen fuel cells and the production of plastics
- deuterium (1P, 1N)
- used in nuclear fusion
- tritium (1P, 2N)
- used in thermonuclear fusion weapons
Nuclide
A type of isotope
- refers to a specific nucleus that contains a certain number of protons and neutrons
Metals (properties in terms of atoms)
Found on the left side of the periodic table (few electrons on their outer shells)
- when they react they lose one or more electrons from their outer shell
- they form positively charged ions (cations)
Non-metals (properties in terms of atoms)
Found on the right side of the periodic table
- when they react they gain one or more electrons onto their outer shell OR they share electrons
- they gain to form negatively charged ions (anions) OR they share to form neutral molecules
Properties of metals (3)
- high melting and boiling points
- good conductors of heat and electricity
- they are all solid (except mercury)
Properties of non-metals (3)
- lower melting and boiling points
- often found as gases
- generally do not conduct heat or electricity
Metal alloys
a mixture of the metals and other materials
- change a metal’s properties
Aluminium (uses)
- a metal alloy
- low density makes it suitable for use in manufacturing aircrafts
- other uses: armour plating for military vehicles
Steel (types and uses)
Alloys of iron that contain carbon and other elements
- high carbon steels: strong but brittle
- uses: making cutting tools and blades
- low carbon steels: soft but malleable
- uses: making car bodies
- stainless steel (contain chromium and nickel): strong and resistant to corrosion
- uses: cooking utensils and cutlery
Bronze (uses)
- an alloy of copper and tin
- adding tin increases the hardness of the material
- uses: making coins, electric hardware and statues
Brass (uses)
- alloy of copper and zinc
- adding zinc makes the material more malleable
- uses: door fitting and water taps
Gold (uses)
- pure gold is soft so jewellers will add other metals like silver, zinc and copper to produce a more resilient substance
- carats provide a measure for the purity of an alloy of gold
- 24 carats = 100%
Ion
An electrically charged atom or group of atoms formed by the loss or gain of one or more electrons
Ionic bond
A chemical bond resulting from the attraction between oppositely charged ions
- found in compounds made between a non-metal and a metal atom
Ionic compound
Composed of positive and negative ions that are combined so that the numbers of positive and negative charges are equal
Metallic bonds
An attraction between positively charged ions and negatively charged, delocalised electrons
- made between at least two metal atoms
Covalent bonds
Bonds created by sharing electrons with other atoms
- made between two non-metal atoms
- found in most non-metal elements and compounds of non-metals
Properties of ionic compounds (name 3)
- high melting and boiling points due to many strong bonds between the ions which takes a lot of energy to overcome
- when they are solids they cannot conduct electricity because the ions are held in place
- when they are liquid or dissolved in water they can conduct electricity because the ions are free to move
- they dissolve in water easily
Small covalent molecules
- have weak intermolecular forces meaning they have low melting and boiling points
- often liquids or gases at room temperature
- don’t contain delocalised electrons and so cannot conduct electricity
- e.g. chlorine
Bigger covalent molecules
- bigger molecules attract other molecules with stronger intermolecular forces meaning they have higher melting and boiling points than small molecules
- don’t contain delocalised electrons and so can’t conduct electricity
- e.g. sucrose
Macromolecules
A very large organic molecule composed of many smaller molecules
Properties of giant covalent structures (name 3)
- no specific formula because the structure can be any size
- very high melting points and boiling points because high temperature and a lot of energy is needed to break covalent bonds
- bonds make them solid at room temperature
- have no intermolecular forces because they are just one large molecule
- strength of bonds: strong
- do not conduct electricity
Diamond
- an allotrope of carbon each carbon atom is bonded to 4 other carbon atoms by strong covalent bonds
- creates a giant covalent structure
Properties of diamond (name 3)
- does not conduct electricity because of no delocalised electrons
- insoluble in water
- high melting point because of strong bonds
- hard because of strong bonds
- can be used as a cutting tool for other materials
- lustrous (shiny)
Graphite
- an allotrope of carbon in which each carbon atom forms 3 bonds
- 1 electron from each carbon atom is delocalised
- carbon atoms form layers of hexagonal rings with each layer held together by weak intermolecular forces
Properties of graphite (name 3)
- conducts electricity because of delocalised electrons
- soft since hexagonal layers can slide over one another easily
- makes it useful as a lubricant and as pencil lead
- lustrous
- opaque
- slippery
- high-melting point
- soluble in water
Uses of diamond (name 3)
- jewelery making
- construction (saw blades, drill bits etc.)
- minor industrial applications
- surgeries
Uses of graphite (name 3)
- stationary
- lubricants
- nuclear reactors
- industries
Silicon (IV) dioxide
- tetrahedral macromolecular structure
- each silica atom is covalently bonded to 4 oxygen atoms and each oxygen atom is covalently bonded to 2 silica atoms
- the formula is SiO2
- each oxygen atom has two non-bonded (lone) electron pairs
- localised; cannot move freely
- there are no delocalised electrons
Properties of silicon dioxide (name 3)
- cannot conduct electricity
- rigid and hard
- high melting and boiling point
- is a semi-conductor
