chemistry 1
what is matter made of?
particles called atoms
what do atoms contain?
protons, neutrons and electrons
where is the nucleus?
in the middle of the atom
what is the relative mass and charge of a proton?
1 , +1
what is the relative mass and charge of a neutron?
1, 0
what is the relative mass and charge of an electron?
very small (0), -1
why does the nucleus have a positive charge?
because of the protons
what is the nucleus radius?
1 x 10 (-14)
how much of the mass is concentrated in the nucleus?
almost the whole mass of the atom is concentrated in the nucleus
how do electrons move?
they move around the nucleus in electron shells
why are atoms neutral?
they have the same number of protons and electrons
what does the nuclear symbol of an atom tell you?
its atomic (proton) number and mass number
what does the atomic number tell you?
how many protons there are
what does the mass number tell you?
the total number of protons and neutrons in the atom
how do you find out the number of neutrons?
subtract the atomic number from the mass number
what is an element?
an element is a substance made up of atoms that all have the same numver of protons in their nucleus
what decided what type of atom it is?
the number of protons in the nucleus
what are isotopes?
different forms of the same element which have the same number of protons but a different number of neutrons
what is the relative atomic mass?
an average mass taking into account the different masses and abundances (amounts) of all the isotopes that make up the element
what is the relative atomic mass used for?
because many elements can exist as a number of different isotopes, relative atomic mass is used instead of mass number when referring to the element as a whole
what is the formula to work out the relative atomic mass?
relatice atomic mass= sum of (isotope abundance x isotope mass number) / sum of abundances of all the isotopes
how are compounds formed?
when elements react, atoms combine with other atoms to form compounds
what are compounds?
compounds are substances formed from two or more elements, the atoms of each are in fixed proportions throughout the compound and theyre held together by chemical bonds
what does making bonds involve?
involves atoms giving away, taking or sharing electrons
what is needed to separate the original elements of a compound out again?
a chemical reaction to do this
what is ionic bonding?
a compound which is formed from a metal and a non metal consists of ions. the metal atoms lose electrons to form positive ions and the non metal atoms gain electrons to form negative ions. the opposiye charges of the ions mean that theyre strongly attracted to each other
what are some examples of compounds which are bonded ionically?
sodium chloride, magnesium oxide and calcium oxide
what is covalent bonding?
a compound formed from non metals consists of molecules. each atom shares an electron with another atom
what examples are there of compounds that are bonded covalently?
hydrogen chloride gas, carbon monoxide and water
are the properties of a compound different to the properties of original elements?
yes they are totally different
elements can be represented by symbols and compounds can be represented by what?
formulas
why can mixtures be easily separated?
theres no chemical bond between the different parts of a mixture
name some physical methods of separation?
filtration, crystallisation, distillation and chromatography
what is air a mixture of?
gases, mainly nitrogen, oxygen , carbon dioxide and argon
what are the properties of a mixture?
just a mixture of the properties of the separate parts- the chemical properties of a substance are not affected by it being part of a mixture
what does insoluble mean?
wont dissolve
what did john dalton say about atoms?
they were solid spheres and they made up the elements
what did jj thompson conclude?
atoms werent solid spheres, his measurements of charge and mass showed that an atom must contain even smaller negatively charged particles- electrons, this was called the plum pudding model
what did the plum pudding model show the atom as?
a ball of positive charge with electrons stuck in it
what did ernest rutherford do?
conducted the famous alpha particle scattering experiments, firing positively charged alpha particles at an extremely thin sheet of gold
why couldnt the plum pudding model be right?
the particles didnt pass straight through, some were deflected more than expected and others were deflected backwards
what did rutherford create?
the nuclear model of the atom, a tiny positively charged nucleus at the centre, and a 'cloud' of negative electrons surround the nucleus, so most of the atom was empty space
why couldnt electrons be in a cloud?
they would be attracted to the nucleus causing the atom to collapse
what did niels bohr suggest?
that electrons were contained in shells and they orbit the nucleus in fixed shells and arent anywhere in between
what did rutherford later discover?
the nucleus can be divided into smaller particles which each have the same charge as a hydrogen nucleus, called protons
what did james chadwick discover?
evidence for neutral particles in the nucleus which are now called neutrons
what are the electron shell rules?
1st shell: 2, 2nd shell: 8, 3rd shell: 8
what is the electronic structure of nitrogen (atomic number 7)
2, 5
what is the electronic structure of magnesium (atomic number 12)
2,8,2