atomic structure, stoichiometry (1+2) Flashcards
definitions
element (2)
a substance containing only one type of atom. All the atoms in an element have the same proton number.
atom
the smallest part of an element that can take part in a chemical change
proton
a positively charged particle in the nucleus of the atom
neutron (2)
the uncharged particle in the nucleus of an atom, with the same relative mass as a proton.
electron
negatively charged particle found in orbitals outside the nucleus of an atom.
energy levels
the specific distances from the nucleus corresponding to the energy of the electrons.
What does the fact that 1. electrons are easily attracted to the anode and 2. easily deflected by an electric field tell us?
- Electrons have a negative charge
- electrons have a very small mass
what is the mass of an electron
1.67*10^-27kg
whats the charge on an electron
1.6*10^-19 C
atomic number
the number of protons in the nucleus of an atom (A)
isotopes
atoms of the same element with different mass numbers.
Why do isotopes have similar chemical properties?
because they have the same number of valence electrons
why do isotopes have different physical properties?
because they have different numbers of neutrons which cause small differences in mass or density
what are the 4 uses of radioactive isotopes?
- check for leaks in oil or gas pipelines
- check thickness of paper
- medicine- treat cancer
- check activity of thyroid gland in throat
electronic configuration
a way of representing the arrangement of the electrons in atoms
first ionization energy
the energy required to remove 1 mole of electrons from 1 mole of atoms of an element in the gaseous state to form one mole of gaseous ions.
what are the key points when writing equations for successive ionization energies?
- atoms and ions are in the gaseous states
- The charge on the ion on the right hand side gives the number of the IE
what do big differences between some successive IEs indicate ?
These large changes indicate that for the second of these 2 IE’s, the electron is being removed from a principal quantum shell closer to the nucleus
why do successive IEs increase across a period?
the successive IE increases, because the net positive charge on the ion gets greater as each electron is removed, there is a greater attractive force between protons and electrons, hence more energy is needed to overcome these attractive forces.
how does the size of the nuclear charge influence IE?
in general, IE increases as proton number/ nuclear charge increases
how does distance of outer electrons from the nucleus influence IE?
In general the further the outer electron shell is from the nucleus, the lower the IE.
how does the shielding effect influence the IE?
In general, the IE is lower as the number of full electron shells between the outer electrons and the nucleus increases.
what is the shielding effect
the ability of inner shell electrons to reduce the effect of the nuclear charge on outer shell electrons.
subsidiary quantum shells
regions of the principal quantum shells where electrons exist in defined areas associated with particular amounts of energy.
atomic orbitals
regions of space outside the nucleus that can be occupied by a max of 2 electrons.
spin pair repulsion
pairing the spinning electrons so they spin in opposite directions reducing the repulsion.
free radical
a species with one or more unpaired electrons.
atomic radius
half the distance between the nuclei of 2 covalently bonded atoms of the same type.
trend in atomic radius
atomic radius increases down any group
atomic radius decreases across any period
trend in ionic radius
ionic radius increases down any group
ionic radius decreases across any period
general trend in IE across a period and why
IE increases across a period because -
1. nuclear charge increases
2. distance between nucleus and outer shell remains constant
3. shielding remains constant
why is there a rapid decrease in IE between the last element in one period and the first element in the next period?
because-
1. the distance (nucleus and outer shell) increases
2. shielding increases
3. these 2 factors cancel out increase in nuclear charge
relative isotopic mass
the mass of a particular atom of an isotope compared to the value of the unified atomic mass unit
relative formula mass
the weighted average mass of one formula unit compared to the value of the unified atomic mass unit.
relative atomic mass
the weighted average mass of atoms in a given sample of an element compared to the value of the unified atomic mass unit
water of crystallization
a specific number of moles of water associated with a crystal structure
hydrated compound
compound which contains a definite number of moles of water in their structure
anhydrous compound
compound containing no water of crystallization
use of mass spectrometry
measure the mass of each isotope present in an element
calculation of Ar from mass spectra
Ar= (isotopic mass * percentage abundance) / 100
calculation of no. of carbon atoms
n= 1.1abundance of M+1 / 100abundance of M
how to identify bromine presence in an organic compound
If the peak heights are equal, there is one atom of bromine per molecule
how to identify chlorine presence in an organic compound
if the peak heights are in the ratio 3(M) to 1(M+2) there is one atom of chlorine per molecule
mole
the amount of substance which contains 6.023*10^23 specified particles.
unified atomic mass unit
one twelfth of the mass of a carbon-12 atom
