ATOMS

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ATOMS ELEMENTSCOMPOSITION AND MASS
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ATOMIC COMPOSITION

• Protons
• electrical charge
• mass 1.672623 x 10-24 g
• relative mass 1.007 atomic mass units
  (u)
• Electrons
• negative electrical charge
• relative mass 0.0005 u
• Neutrons
• no electrical charge
• mass 1.009 u

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ATOM COMPOSITION
The atom is mostly empty space

• protons and neutrons in the nucleus.
• the number of electrons is equal to the number of
  protons.
• electrons in space around the nucleus.
• extremely small. One teaspoon of water has 3
  times as many atoms as the Atlantic Ocean has
  teaspoons of water.

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Atomic Number, Z

• All atoms of the same element have the same
  number of protons in the nucleus, Z

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Al
26.981
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Isotopes

• Atoms of the same element (same Z) but different
  mass number (A).
• Boron-10 has 5 p and 5 n 105B
• Boron-11 has 5 p and 6 n 115B

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Hydrogen Isotopes
Hydrogen has _____ isotopes
11H
__ proton and __ neutrons, protium
21H
__ proton and __ neutrons, deuterium
31H
__ proton and __ neutrons, tritium radioactive
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Isotopes Their Uses
Heart scans with radioactive technetium-99.
9943Tc Emits gamma rays
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Isotopes

• Because of the existence of isotopes, the mass of
  a collection of atoms has an average value.
• Average mass ATOMIC WEIGHT
• Boron is 19.9 10B and 80.1 11B. That is, 11B
  is 80.1 percent abundant on earth.
• For boron atomic weight
• _____ (_____ u) _____ (_____ u) _____ u

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Masses of Isotopesdetermined with a mass
spectrometer
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Mass spectrum of C6H5Br
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Isotopes Atomic Weight

• Because of the existence of isotopes, the mass of
  a collection of atoms has an average value.
• 6Li 7.5 abundant and 7Li 92.5
• Atomic weight of Li ______________
• 28Si 92.23, 29Si 4.67, 30Si 3.10
• Atomic weight of Si ______________

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Atomic Weight

• The mass of one atom of an element relative to
  one atom of another element.
• OR the mass of 1000 atoms of one relative to
  1000 atoms of another.
• For example, an O atom is approximately 16 times
  heavier than an H atom.
• Define one element as the standard against which
  all others are measured
• Standard carbon-12
• C atom with ____ protons and ___ neutrons is the
  mass standard
• C-12 12 atomic mass units (u)
• 1 u 1/12th the mass of a carbon-12 atom

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Counting Atoms

• Mg burns in air (O2) to produce white magnesium
  oxide, MgO.

How can we figure out how much oxide is produced
from a given mass of Mg?
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Counting Atoms

• Chemistry is a quantitative sciencewe need a
  counting unit.

MOLE
1 mole is the amount of substance that contains
as many particles (atoms, molecules) as there are
in 12.0 g of 12C.
518 g of Pb, 2.50 mol
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Particles in a Mole
Avogadros Number
Amedeo Avogadro 1776-1856

• 6.02214199 x 1023

There is Avogadros number of particles in a mole
of any substance.
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Molar Mass

• 1 mol of 12C _______ g of C _______
  atoms of C
• 12.00 g/mol of 12C is its MOLAR MASS
• Taking into account all of the isotopes of C, the
  molar mass of C is ______ g/mol

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One-mole Amounts
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MOLAR CONVERSIONS
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PROBLEM How many moles of Mg are represented by
0.200 g?

• Mg has a molar mass of ___________.

How many atoms in this piece of Mg?
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PROBLEM What is the mass of 4.2 x 1023 atoms
of sodium?
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MOLAR CONVERSIONS
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PARTICLESatoms molecules formula units
MOLES mol
MASS g
6.02 x 10 23 particles/mol
g/mol
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?
22.4 L/mol
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VOLUMEof gas _at_STP L