nature of chemistry 1 Flashcards
Chemistry
study of matter, interactions involves experimenting in macroscopic world and theorizing about microscopic world
Empirical knowledge
comes from investigation and observation
Theoretical knowledge
Explains scientific observation: based on ideas created to explain
Theory
explanation /model based on observation reasoning experimentation
- why something happens
predicting
Law
explain observation either as statements or mathematical equation
-proven consistently
What did greek philophers discover?
- matter can be subdivided into tiny particles calle atomos(cant be cut )
Democritus
atom exsistence
different sizes,constant motion
Aristole
matter is made up of earth, water ,fire, air
Dalton
Law of conservation of mass
- atoms are rearranged to form new substances but never created or destroyed
JJ thompson
-used a cathode ray tube to discover the existence of electrons
- electrons are small (-) particles(plum pudding model)
Rutherford
nuclear model
- aimed + alpha particles at gold foil and measured how many alpha particles deflected off the foil on a fluorescent screen
COnclusions:
most were absorbed by foil and only some were deflected
Nuclear model: atom contains small dense positive centre
Chadwick
Exsistnece of the neutron confirmed
Bohr
Electrons existed in energy levels
Planetary model: electrons orbit the nucleus in definite energy levels (shells) can jump and transfer.
Ground state
when electrons in an atom have the lowest amount of energy possible for the location that they are at in the element
Excited state
when energy is added in the form of heat or electricity to an atom
electrons absorb energy which allows them to jump to a higher energy level
Emission spectrum
pattern of electron movement= ands of certain wavelengths of coloured light
- used to identify unknown samples
purple= far electron jump
red= short electron jump
Isotope
atoms of the same element that have different # of neutrons but same p and e-
isotopic abundance
the % of a given isotope in a sample of an element
Radiation and radioisotopes
- some isotopes are stable while others break
- difference in stability is due to the composition of the nucleus
- large # of neutons destabilize the nucleus
Alpha particles
same structure as helium nucleus with a 2+ charge
- blocked by paper
Beta particles
-negatively charged e-
- blocked by aluminun
gamma rays
have no mass and travel at light speed blocked by lead
trend
predictable change in particular direction
electron shielding
inner electrons shield outer electrons from the full attractive force of the nucleus(protects valence shall from attraction
effective nuclear charge
charge felt by valence electrons after you have taken into account the # of shielding electrons
atomic radius
distance from center to outmost orbit
what happens to atomic radius as you move down the group ?
it increases as the electrons occupy consecutiveley higher energy levels farther from nucleus
- ENC decreases due to increased shielding
what happens as you move across a period to radius?
atomic radius decreases
- same number of orbits electrons are in same energy level
-more nuclear charge (protons added moving left to right)
- outermost electrons are pulled closer
what happens when you move down a group to ionization?
what happens when you move across a period?
decreases due to increased electron shielding and decreased ENC
- increases as you move across period, increas in ENC unchanged shielding
Electron affinity
the energy given off when an electron is added to atom to make an anion
- high affinities form negative ions in IC
- low affinities form positive ions in IC
EA trends
- decreases as you move down group due to increased electron shielding and decreased ENC
- increases as you move across a period
due to increasing nuclear charge unchanged shielding easy to gain e-
Electron negativity
measure of the ability of an atom in a compound to attract electrons in a bond
- higher electronegativity means a stronger pull on e-
- charges vary from 0-4
Radius of cations
-metals form cations
- cations form by losing electrons
- cations smaller then og atom as they lose an energy level
- more e- lost = radius gets smaller
- enc increases, shielding decreases.
radius of anions
-nonmetals form anions
- anions form by gaining electrons
- anions are bigger then og atom
- have the same energy level and nuclear charge but more repulsion
- radius get larger
ENC decreases shielding unchanged repulsion increases
Ionic radius trends
-increases as you move down a group
- decreased ENC as shielding is unchanged
- decreases as you move across a period due to inccreasing nuclear charge
- + ions left to right =higher ENC
- - ions left to right ( less electrons are need to the right so e- and p count similar = less repulsion
ionization energy
energy required to remove an electron from an atom or ion
- overcome attraction between e- and nucleus+
2nd ionization energy
the energy required to remove a second electron from a cation
- needs more energy then 1st ionization as the nucleus became more + since first electron was lost
ionization energy group 1
group 1: easily loses its 1 valence e-
- low first ionization energy
- second ionization will be very high since the new valence is full
ionization group 2
- easily loses 2 valence e -
- low first and second ionization energies
- high third ionization energy since new shell is full
Electronegativity trends
- decreases as you move down a group due to decreases ENC and lots of shielding
- increases as you move across a period
increasing atomic #, increase in ENC and unchanged shielding
metals have low electronegativity
nonmetals have high electronegativity
dmitri medeleevs periodic law
when elements are arranged according to increasing atomic mass , periodic recurrence of properties occurs at regular intervlas
Alkali metals
- column 1, 1 valence e-
- soft, silver, solids
- reacts violently to make base
Alkaline earth metals
- column 2, 2 valence e-
- solid
- reacts with air to form oxide coatings
- reacts with hydrogen to form hydrades
halogens
column 17 , 7 valence e-
- solid, liquid, gas
- dull and not a conductor
- very reactive
noble gases
column 18 8 valence e-
- gases
- low melting and boiling point
- inert (unreative)
