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CHEM MIDTERM TOPIC 1-THE ATOM

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daltons atomic theory
1. all elements are composed of individual atoms
2. all atoms of an element are identical
3. atoms of different elements are different and have different masses
4. compounds are formed by the combination of atoms of different elements
is daltons atomic theory entirely true?
no
what part of dalts atomic theory is wrong
atoms are not indivisible but they are made up of smaller parts
Thomson
used a cathode ray tube to show one of these smaller units that make up an atom
-proved that there was a negative charge
-theorized that an atom contains small, negatively charged particles called electrons
plum pudding model
model where the electrons were embedded in the atom and the mass of the rest of the atom was evenly distrubed and positively charged, taking up all of the space not occupied by the electrons
-not true
Rutherford
-alpha ray throguh the piece of gold foil
-most of the particles passed straight through the foil, and a few were slightly deflected
-concluced that the atoms have a dense central core, called the nucleus, and the rest of the atom is mostly empty space
-because alpha particles are positively charged and were repelled by the nucleus, the nucelus must also be positively charged becasue like charges repel each other
bohr's atom
-the planetary model
a dense nucleus with electrons found in the surrounding circular orbits
what is the modern model of the atom?
the wave-mechanical model
wave-mechanical model
-atom has a dense, positively charged nucleus
-electrons have distinct amounts of energy moving in orbitals
orbitbal
a region in which an electron of a particular amountof energy is most likely to be located
properties of a proton
1+ charge
mass=1 AMU
location=nucleus
properties of neutrons
0 charge
mass=1 AMU
location=nucleus
properties of electron
-1 charge
mass= 1/1836 AMU
location=outside the nucleus
atomic number
number of protons in the nucleus
mass number
um of the number of protons and neutrons in the nucleus
isotopes
atoms of the same element that have different numbers of neutrons, and hence have different mass numbers
how are isotopes identified and give an example using carbon
indicites both the element and its mass number
ex. C-12 (12 is the mass number)
ex. carbon 14
14 C
6
atomic mass
average mass of all the isotopes in a sample of the element
ground state
when the electrons occupy the lowest available orbitals
excited state
the unstablue condition when electrons may absorb energy from an outside source and temporarily move to a higher energy level.
df
df
what do electrons produce
lights on the bright line spectrum
how do you calculate the atomic mass of an element if you have the percentages of its isotopes and their atomic masses
Convert the percentages to decimals, multiply it by the mass of that isotope, and add those masses together
ex. c-12 98.89%
c-13 1.108%

12 AMU X .9889= 11.87 AMU
13 AMU X .01108= 0.1440 AMU

11.87+0.1440= 12.01 AMU
hunds rule
a single electron must be placed into each orbital of a given sublevel before any pairing takes place
how many electrons go into the first enegy level
2
how many eletrons go into the second energy level
8
how many electrons go into the third energy level
18
how many electrons go into the 4th energy level
32
electron holdings (s, p, d, f)
s- 2
p- 6
d- 10
f- 14
what is the irregularity in the order of electron orbitals?
4s comes before 3d because of an overlap
homogenous
uniform throughout
can contain more than one particle but they are evenly mixedd
heterogenous
made up of parts with different chemical and physical properties
-not uniformly mixed or dispersed
pure substance
matter whos compisition is the same throughout the sample
elements
substances that can be broken down or decomposed into simple substances by chemical means
compounds
composed of one or more elements that are chemically combined in definite proportions by mass
-the composition is the same throughout
law of definite proportions
types of atoms in a compound exist in a fixed ratio
mixtures
combinations of two or more pure substances that can be separated by physical means
-their composition is not definite or fixed
solutions
homogenous mixtures

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