chapter 2 atoms and elements Flashcards
Atoms
- smallest identifiable unit of an element
- about 91 naturally occurring elements
- -about 20 synthetic
- exact # is ambiguous
Law of Conservation of Mass
In a chemical reaction, matter is neither created nor destroyed.
* total mass after reaction does not change
Law of Constant Composition /definite proportions
all samples of given compound, regardless their source/how they are prepared have same proportions of constituent Element.
Ex: mass ratio: 16g Oxygen/2.0g Hydrogen= 8.0 or 8:1
Law of Multiple Proportions:
when 2 elements (A&B) form 2 different compounds, the masses from element B that combine with 1g of element A can be expressed as a ratio of small whole numbers.
EX: CO2 carbon dioxide:
mass O combines with 1g C= 2.67g
CO Carbon monoxide
mass O + 1g C= 1.33g
Mass O to 1g in CO2/Mass O to 1g in CO= 2.76g/1.33g=2.0
ratio: 2:1
Atomic Theory (John Dalton, 1808)
- each E is composed of tiny, indestructible particles called Atoms
- all atoms of given E have same mass & other properties that distinguish them from atoms of other E
- atoms combine in simple whole number ratios to form compounds.
- atoms of one E cant change into another E. in a chem reaction atoms change the way they are bonded together w/ other atoms to form new substance.
Cathode Ray
produced when high elec voltage is applied between 2 electrodes w/in a partially evacuated glass tube.
Tube: cathode ray tube
electrical charge
negative
fundamental property of some of the particles that compose atoms
attractive/repulsive forces
electrostatic forces
Electron
neg. charge low mass particle
present in all atoms
charge: -1.6x10^-19 C
Plum Pudding Model- JJ Thompson
Neg charged e- are held together by a (+) charged sphere
Radioactivity
emission of small energetic particles from core of certain unstable atoms
Rutherford (1871-1937)
Gold foil experiment
- alpha particles to gold foil
- most pass through with no detection
- proved plum pudding model was wrong
- some particles were deflected/ bounced back
Nuclear Theory (Rutherford)
- most atoms mass/pos (+) charge are contained in the core (nucleus)
- most volume of atom is empty space, throughout which tiny neg (-) electrons are dispersed
- there are many e- outside of nucleus. (+) particles in nucleus (protons) atom = neutral
Neutrons
neutral particles in nucleus
Atomic Mass Unit (amu)
1/2 mass of C atom
containing 6 protons & 6 neutrons
*mass of 1 p or n = 1 amu
*proton (p)= 1.67262x10^-27 kg (+1 relative charge)
*neutron (n)= 1.674493x10^-27 kg (0 rel charge)
*electron (e-)= .00091x10^-27 kg (-1 rel charge)
Atomic Number
# of protons in atom nucleus defines element
Chemical Symbol
one or two letters abbreviated for element
- listed below atomic # on periodic table
Isotopes
atoms w/ same number of protons but different # of neutrons
Natural Abundance
relative % of particular isotopes in a naturally occurring sample w/ respect to other isotopes of same element
Mass number
sum of protons and neutrons
Ions
losing or gaining electrons (e-)
Cations
positivly charged ions
lose electrons
EX: Li+
Anions
Negatively charged ions
gain electrons
EX: F-
Periodic law
when elements are arranged in order of increasing mass, certain sets of properties recur periodically
- mass increases left to right
- rows = similar properties
Metals
left side/ middle period
- Properties: good conductors of heat/ electricity
- can be pounded into flat sheets
- drawn into wires
- often shiny
- tend to lose e- in chem reactions
- properties tend to be less predictable based on location
Non metals
upper right side
varied properties
poor conductors of heat/ electricity
tend to gain e- when undergo chem reaction
Metalloids
some= semi conductors
mixed properties
intermediate elec. conductivity
Main group elements
properties tend to be largely predictable based on position on periodic table
Family
column w/in main group
Nobel Gases
- group 8a
- mostly unreactive
- chemically stable
Alkali Metals
- reactive metals
- group 1A
EX: Na is violent when in water
Alkaline Earth Metals
- group 2A
- reactive but not as much as group 1A
Halogens
- group 7A
- very reactive non metals
ex: Cl (chlorine)
Atomic Mass
calculated average mass
- average mass of isotopes that compose element “weighted according to natural abundance of each isotope”
Mole
amount of material containing
6.022x10^23 particles
(Avogadro’s number)
-value of mole = number of atoms in exactly 12g C of pure C-12
-relationship between mass & # of atoms
-count atoms by weighing them
conversions :
1mol/ 6.022x10^23 atoms or 6.022x10^23 atoms/ 1mol
Molar Mass
mass of 1 mol of atoms of an element
measurement = g/mol is numerically equal to atomic mass in amu
Scanning Tunneling Microscopy
- image and move individual atoms/ molecules
- extremely sharp electrode over surface & measuring the resulting “tunneling current”
