Topic 3 Flashcards
Element
A pure substance made up of only one type of atom
Compound
A pure substance made up of 2 or more types of atoms, chemically bonded
Mixture
Two or more different pure substances physically combined
Atom
The smallest particle of an element that keeps the identity of the element
Molecule
Two or more atoms covalently bonded together
Ion
An electrically charged atom or molecule
Physical properties of metal
All solid metals have the following properties:
1. They are lustrous (shiny) when pure
- They are very good conductors
- The delocalized mobile electrons can form an electric current - They are very good thermal conductors
- The delocalized electrons transfer heat quickly and closely packed cations transfer heat when vibrating - They are malleable (can be beaten into shapes)
- They are ductile (can be stretched into wires)
- They have variable melting points.
Metallic bonding
Metals have a 3D giant metallic structure, consisting of a lattice of closely packed cations in a ‘sea’ of delocalized valence electrons.
Metallic bonding is the force of attraction between the cations and the delocalized electrons.
The strength of the metallic bonding varies between different metals.
It is found in metallic elements or alloys
Graphite structure and properties and uses
Each C atom is covalently bonded to only 3 other C atoms in a 2D hexagonal layered arrangement.The 4th electron of each C atom is not involved in bonding. These electrons are delocalized (able to move freely throughout the whole structure)
- Non-volatile – strong covalent bonds require large energy to break
- Flaky and brittle – layers of C atoms can slide over each other because of weak forces between layers
- Electrically conductive – delocalized electrons can form an electric current
USES: - As a solid lubricant (a substance which reduces friction) between machine parts
- As electrodes in electrical cells.
- In pencils and crayons. The layers easily slide off with friction.
Diamond structure and properties and uses
Each C atom is covalently bonded to 4 other C atoms in a 3D tetrahedral arrangement.
PROPERTIES:
1. Non-volatile - very strong covalent bond require large energy to break
2. Extremely hard (hardest known material) – very strong covalent bonds and a symmetrical arrangement of atoms
3. Electrical insulator – no mobile charged particles
USES
1. In cutting tools and drill bits (It can cut through all other materials)
2. In jewelry (shiny)
Giant covalent structures
These are giant structured substances made up of huge numbers of atoms held together by covalent bonds. They are also called macromolecules. Some elements have a giant covalent (or macromolecular) structure.
Diamond + graphite
Simple covalent compounds
2 (or more) different non-metallic elements can chemically combine to form simple covalent (or molecular) compounds.
Covalent bonding
Non-metallic elements can also achieve a full valence shell by sharing electrons.
A pair of electrons shared between 2 atoms creates a single covalent bond
Double, then triple
Structure of giant ionic compounds
Each ion is surrounded and bonded to ions of opposite charge in an ionic lattice (a 3D repeating regular arrangement of huge numbers of alternating cations and anions).
Ionic bonding
When atoms of metallic elements lose electrons to form cations, the electrons are gained by the atoms of non-metallic elements to form anions.
(The ions formed always have the same electron structure as a noble gas)
The oppositely charged ions attract each other to form ionic bonds that hold the ions together. This produces an ionic compound (metal and non-metal).
Name the number of protons and neutrons in Boron-11 (it has 5 electrons)
The number after the name refers to the nucleon number (e.g. Hydrogen-1, Hydrogen-2, Boron-10, or Boron-11). Usually, one isotope is far more common than the rest: Hydrogen-1 makes up 99% of hydrogen.
Thus proton = 5
Neutron = 6
This is an isotope btw
Atomic number
-> Atomic number (proton number) of an element is the number of protons each atom of the element has in its nucleus (on top of chemical symbol in IGCSE periodic table
Nucleon number
The nucleon number (mass number) is the combined number of protons and neutrons in the nucleus of an atom (bottom of the chemical symbol in IGCSE periodic table)
This can vary in the same element because there can be different numbers of neutrons (isotopes, see subtopic 2 topic 3).
Thus, number of neutrons = Nucleon number – Atomic number
