CHEM MIDTERM TOPIC 1-THE ATOM
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- daltons atomic theory
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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
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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
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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
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-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
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-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
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-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
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1+ charge
mass=1 AMU
location=nucleus - properties of neutrons
-
0 charge
mass=1 AMU
location=nucleus - properties of electron
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-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)
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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
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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
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combinations of two or more pure substances that can be separated by physical means
-their composition is not definite or fixed - solutions
- homogenous mixtures