Key concepts in chemistry Flashcards
Where are metals located in the periodic table?
On the left side of the table, wiht the dividing line going from under Al to Ts
Uncommon formulae
Iodine = I2 Bromine = Br2 chlorine, Cl2 fluorine, F2 oxygen, O2 nitrogen, N2 hydrogen, H2
What is a chemical union of two or more elements called?
Compound
Define ionic compounds
A compount where atoms are joined together with ionic bonds. Usually contain at least one metal and one non metal.
Define ion
An ion is a charged particle when an atom gains or loses electrons
Daltons model
Published in 1803, he thought that all matter was made of atoms which he imagined as tiny solid balls. He thought atoms could not broken down any further, the atoms of a given element are identical to eachother, during chemical reactions atoms rearrange to make different substances. Daltons model has changed over time because of the discovery of sub atomic particles.
Masses of particles
Proton = 1 Neutron = 1 electron = 1/1835
Calculating number of subatomic particles rules.
Number of protons = atomic number
Number of electrons = Atomic number
Number of neutrons = mass number - atomic number
Define isotopes
Atoms of the same element that have different numbers of neutrons in their nuclei.
Mendeleev’s Periodic table
He organised elements in order of increasing relative atomic mass. He noted chemical properties of the elements and their compounds showed a periodic trend. He arranged the elements by putting them with others that had similar chemical properties. He left GAPS for undiscovered elements. He predicted elements that had not been found yet by seeing what would fit next to other elements in the gap
Define atomic number.
Number of protons in the nuclei
Why do atoms have similar properties when they are in the same group?
The number of electrons on the outer shell is the same, so they are similar.
Covalent bonds
When atoms share electrons between them. Usually non metals.
Definition of a molecule
A group of two or more atoms joined together by covalent bonds. They will always contain the same number of atoms in each element.
Dot and cross diagrams
The outer shell is drawn as a circle - circles overlap when there is a covalent bond. Electrons from one atom are drawn as dots and electrons from the other are drawn as crosses.
Giant Covalent structures
Covalent bonding leads to the formation of molecules: these are either simple molecules which contain a set amount of atoms joined by covalent bonds or Giant Covalent substances which contain many atoms joined together by covalent bonds. EG: SILLICA- Main compound found in sand, it is a giant covalent substance.
Properties of giant covalent structures
High melting points, Conduction of electricity, Insoluable in water.
Diamond and Graphite properties
Different forms of carbon. Joined together by 4 other carbon atoms by covalent bonds. Diamond is a giant covalent substance joined to 4 carbon atoms, tetrahedral network structure and there are no free electrons.
Graphite is also a giant covalent structure- Joined to 3 other carbon atoms, hexagonal layered network, each carbon atom has one un-bonded outer electron.
Delocalised electrons
Free to move through the structure of graphite, so graphite can conduct electricity. Makes it useful for electrodes in batteries and for electrolysis. Layers in graphite can slide over one and other as the forces between them are weak.
Metals vs Non metals
Metals are on the left hand side of the periodic table - Non metals are on the right. Metals are usually: Shiny, have high melting points, good conductors of electricity and heat, high density and malleable. Non metals: Dull, Low melting points, Poor electicity and heat conductors, low density and brittle
Exceptions to the metal/non metal rules
Mercury has a low melting point, graphite has a high melting and boiling point and is a good conductor of electricity
Ionic bonds
Metals and non metals - loss and gain of electrons of atoms, ionic lattice structure
Simple bonds
Non metals - Shares pairs of electrons between atoms, small group of atoms held together, a molecular structure
Giant covalent
Non-Metals
Share pairs of electrons between atoms
Billions of atoms are held together
Giant covalent lattice strucrure
Metallic bonds
Metals
Outer electrons free to move
Billions of positive metal ions, giant metallic lattice structure
Calculations
Avogadro’s constant - 6.02 x 10^23
Mass in (g) = Mr x Number of moles of mass = Mr x Mol
