Key concepts in Chem Flashcards
Structure of an atom
It’s made up of 3 subatomic particles.
- in nucleus contains protons and neutrons
- majority mass of atom is found in its nucleus
- electrons orbit the nucleus and have negative charge
history of atom
- Dalton – everything made from atoms, cannot be created, divided or destroyed , atoms join together to make new substances - atoms of the same element are the same, atoms of different elements are different
- Thomson – used cathode-ray tube to discover atoms can be divided into smaller parts, beam moved from negatively charged plate to positively charged plate- knew that the particles must have a negative charge, plum pudding- negative electrons scattered throughout positively charged material
- Rutherford– shot beam of positively charged particles into gold foil some particles continued in straight line others deflected to side and some bounced back
- new model that most of atoms mass is in the centre called nucleus
- model is mainly empty space, electrons travel in random paths around nucleus
- Bohr final model– electrons orbit nucleus in fixed positions ( orbitals)
Why do atoms have an equal number of protons and electrons ?
Atoms are neutral because the charge on a proton is 1+ and an electron is 1-, so they must be equal so they can cancel each other out
Size and mass of a nucleus
Nucleus of atom is very small compared to size of entire atom, but most of its mass is concentrated there
What are isotopes ?
- elements that have the same number of protons, but different number of neutrons
relative atomic masses equation (e.g. Cl)
75% of 35 Cl
25% of 37 Cl
(75x35 + 25x37) / 100 = 35.5
- this is the relative atomic mass of chlorine in the periodic table
How to calculate relative atomic mass
- Relative atomic mass is calculated using the abundance of different isotopes, because it’s an average can lead to R.A.M. not being whole number
- atomic number and mass number will always be whole- they’re not averages
Mendeleev’s arrangement of periodic table
- ordered the table in order of atomic mass, left gaps for elements that hadn’t been discovered yet
- realised elements w/ similar properties belonged in the same groups– elements later discovered w/ properties that fit the gaps were added
- arrangement wasn’t in order of increasing R.A.M., because it didn’t take into account of isotopes
Arrangement of elements in periodic table
- elements arranged in order of increasing atomic number – in rows called periods
- elements w/ similar properties are placed in the same vertical columns called groups
How to write electronic configuration (e.g. Na)
e.g. sodium has 11 electrons 2 on inner shell, then 8 and then 1 on its outermost shell
so the arrangement is 2.8.1
How electronic configuration is related to position on periodic table ?
- groups an element is in tells you how many electrons are on outermost shell
- period an element is in tells you which number of shells an element’s outermost electron is found in
What is an ion?
-an ion is an atom or group of atoms with a positive or negative charge
formations of ions in ionic compounds
periodic table
-group 1 metals will lose 1 electron and form +1 ions
-group 2 metals will lose 2 electrons and form +2 ions
- group 3 will loose 3 electrons and form 3+ ions
- GROUP 4 DO NOT FORM IONS
- group 6 nonmetals will gain 2 electrons and form 2- ions
- group 7 nonmetals will gain 1 electron and form 1- ions
- a compound will have an overall charge of 0 so you need to balance
out the + and - charges
structure of an ionic compound as lattice structure
- strong electrostatic forces w/ oppositely charged ions
- has regular arrangement of ions
- forces act in all directions
How does covalent bonding occur?
- occurs in most non-metallic elements and in compounds of nonmetals
- When atoms share pairs of electrons, they form covalent bonds. These bonds between atoms are strong
examples of covalent bonds
-consist of small molecules e.g. HCl, H2, O2, Cl, NH3,
CH4
- some have large molecules like polymers
Properties of ionic compounds
-Ionic compounds have regular structures in where there are strong electrostatic forces of attraction in all directions between oppositely charged ions.
- have high melting and boiling points,a lot of energy is required to break the strong bonds.
- When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move (delocalised electrons ) and carry current
- don’t conduct electricity as solids, because the ions are fixed and are not able to move, carrying charge
with them.
- Often dissolve in water to form an aqueous solution
Properties of similar molecular compounds
- low boiling and melting points
- weak inter molecular forces between the molecules
- substances that have small molecules don’t conduct electricity
- many are insoluble in water, but some are soluble
Giant covalent structures
- very high melting points
- some giant covalent structures conduct electricity, but some don’t
Properties of metals
- Have delocalised electrons and so are free to
move through the structure- gives strong metallic bonds - high melting and boiling points
- conduct heat and electricity
- insoluble in water, some will react
Properties of diamond and graphite
Diamond
- very hard
- very high melting point and doesn’t conduct electricity
Graphite
- layers can slide over each other, because no covalent bonds between the layers
- weak inter molecular forces means graphite is soft
and slippery.
What is a polymer ?
- has very large molecules
- have chains of carbon atoms
Properties of non-metals
- low boiling points and poor conductors of electricity
No. of moles equation (mol)
no. of moles = mass/ molar mass
What is the emperical formula ? ( e.g. Fe2O4)
- have a common multiple e.g. Fe2O4 , the empirical formula is simplest whole number ratio, which would be FeO2
- if there is no common multiple, you already have the empirical formula
What is the law of conservation of mass?
-no atoms are lost or made during a chemical
reaction –so mass of the products = mass of the reactants
concentration equation ( mol dm^-3)
concentration = no. of moles ( mol) / volume (dm^3 )
converting volume units from cm^3 to dm^3
- cm^3 to dm^3 – divide by 1000
- dm^3 to cm^3 – multiply by 1000
What is Avogadro’s constant ?
Avogarado’s constant is 6.02x10^23
Explain limiting reactant
In a chemical reaction with 2 or more reactants you will often use one in excess, ensure that all of the other reactant is used
-reactant that is used up / not in excess is called the limiting reactant, it limits the amount of products
