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ATOMS and MOLECULES
Matter is anything that has mass and volume (occupies space).
The amount of
matter measured by its resistance to acceleration (movement)
Mass is a measurement of matter present.
Weight is a measurement of the gravitational force acting on an object.
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
ELEMENTS
Homoatomic molecules of
individual atoms of the same kind
Cannot be chemically subdivided
Into simpler substances.
PURE SUBSTANCE
Matter that has
constant composition
and fixed properties
COMPOUNDS
Heteroatomic molecules of individual
atoms (ions) of two or more kinds
Can be chemically subdivided
into simpler substances
Products of the chemical subdivision are
either elements or simpler molecules
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Symbols and Formulas
An
element is a substance that cannot be broken down into a simpler
form capable of an independent existence as observable matter.
An
element is homogeneous pure substance
made up of identical
atoms.
115 different elements known
115 different kinds of atoms
Α ΤΟΜΟΣ
88 elements found in nature
27 elements man made The word "atom" comes from the Greek
a-tomos, meaning "un-cut-able"
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Symbols and Formulas
Elements you already know:
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Gold
Oxygen
Iron
Aluminum
Copper
Helium
Mercury
Hydrogen
Lithium
Calcium
Sodium
Potassium
Neon
Fluorine
Chlorine
Silver
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Symbols and Formulas
Elements you already know:
Latin: aurum
Latin: ferrum
Latin natrium
Latin: kalium
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Gold Au
Oxygen O
quicksilver
Iron Fe
Aluminum Al
Copper Cu Latin: cuprum
Helium He
Mercury Hg hydrargyrum
Hydrogen H
Lithium Li
Calcium Ca
Sodium Na
Potassium K
Neon Ne
Fluorine F
Chlorine Cl
Silver Ag Latin: argentum
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Symbols and Formulas
Compound is a pure substance consisting of two or more kinds
of atoms in the form of heteroatomic molecule of individual atoms.
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Symbols and Formulas
Compound is a pure substance consisting of two or more kinds
of atoms in the form of heteroatomic molecule of individual atoms.
Compound formula is a symbol for the molecule of a compound,
consisting of the symbols of the atoms found in the molecule.
H 2O
CO
CO2
NaCl
C 3H 8
propane
C 9 H 8 O4
aspirin
C5H8NNaO4
monosodium glutamate (MSG)
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Inside the Atom
19th
Extensive experimental evidence (since
century) indicates that atoms are made up of
many smaller particles.More than 100 subatomic
particles have been discovered.
Most of the chemical behaviour of matter can be
explained with the three fundamental particles:
PROTON, NEUTRON and ELECTRON.
He, Helium
1Å = 1 x 10-8 m
Every atom has two basic parts:
He
2p+ 2n 2e-
nucleus (core)
“shell” (“electron cloud”)
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Inside the Atom
Extensive experimental evidence (since 19th century) indicates
that atoms are made up of many smaller particles.
More than 100 subatomic particles have been discovered.
Most of the chemical behaviour of matter can be explained with the
three fundamental particles: PROTON, NEUTRON and ELECTRON.
Atoms are composed of protons, neutrons, and electrons, whose properties are shown below:
mass, g
mass, µ
charge
electron
9.07 × 10–28
5.49 × 10–4
1–
proton
1.67 × 10–24
1
1+
neutron
1.67 × 10–24
1
0
particle
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Chemistry 21A
symbol
–1
1
0e,
e, e-
0H+, 0p,
1
1
0n,
p, p+
n
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Inside the Atom
9Be
(Berillium)
4 protons
4 electrons
5 neutrons
U.S. Atomic Energy Commission Shield
mass, g
mass, µ
charge
electron
9.07 × 10–28
5.49 × 10–4
1–
proton
1.67 × 10–24
1
1+
neutron
1.67 × 10–24
1
0
particle
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Chemistry 21A
symbol
–1
1
0e,
e
0H+, 0p,
1
1
0n,
p, p+
n
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Isotopes
He, Helium
ATOMIC NUMBER, Z, is equal to the
number of protons in the nucleus of an atom.
MASS NUMBER, A, is equal to the
sum of protons and neutrons in an atom.
p=?
n =?
e =?
1Å = 1 x 10-8 m
He
2p+ 2n 2e-
Z=2
A = 4 (2p + 2n)
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Isotopes
ATOMIC NUMBER, Z, is equal to the
number of protons in the nucleus of an atom.
MASS NUMBER, A, is equal to the
sum of protons and neutrons in an atom.
The mass spectrum of magnesium
shows three isotopes of masses
24 through 26 having the natural
abundances shown on the plot.
Of the 92 natural elements,
23 have only a single isotope,
and are said to be monoisotopic.
ISOTOPES are atoms that have the
same atomic number (number of protons) but
different mass numbers (number of neutrons).
Greek isos = "equal", tópos = "site, place"
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Isotopes
nuclide
symbol
range of natural
Z (p)
N(n)
isotopic mass (µ)
variation
half-life
(mole fraction)
12
C
6
6
12 by definition
STABLE
0.98853-0.99037
13
C
6
7
13.0033548378(10)
STABLE
0.00963-0.01147
14.003241989(4)
5.70(3) x 103
years
<10-12
14
C
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6
8
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Relative Masses of Atoms and Molecules
Relative masses provide a simple way
of comparing the masses of atoms.
atomic mass unit (µ) is defined as
1/12 of the mass of one atom of
carbon-12, (1.661 x 10-24 g)
The unified
µ
The atomic masses of other elements can be converted in a similar way
The measured atomic mass of a 31P atom is 5.143 x 10-23 g
5.143 x 10-23 g
Conversion to atomic mass units gives -------------------------- = 30.974 µ
1.661 x 10-24 g
31P
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atom is 30.974 µ
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Relative Masses of Atoms and Molecules
Molecules are made of atoms, so the relative mass of
molecule can be calculated by adding together the
atomic weights of the atoms that make up the molecule.
MOLECULAR WEIGHT is the relative mass of
a molecule expressed in atomic mass units (µ)
and calculated by adding together the atomic weights
of the atoms that make up the molecule.
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Relative Masses of Atoms and Molecules
Molecules are made of atoms, so the relative mass of
molecule can be calculated by adding together the
atomic weights of the atoms that make up the molecule.
MOLECULAR WEIGHT is the relative mass of
a molecule expressed in atomic mass units (µ)
and calculated by adding together the atomic weights
of the atoms that make up the molecule.
What is the molecular weight of sulfuric acid, H2SO4?
Solution: The atomic weights of hydrogen and of oxygen are 1.01 and 16.00, respectively
From a table, you can find that the atomic weight of sulfur is 32.06.
Adding everything up, we have
2xH
S
4 x O
(2 x 1.01) + 32.06 + (4 x 16.00) = 98.08
The molecular weight of sulfuric acid, H2SO4 is 98.08
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Isotopes and Atomic Weights
For elements with more than one isotope, the atomic
mass (atomic weight) reported in the periodic table
represents a weighted average of the atomic masses of
the naturally occurring isotopes
In other words, it’s the weight of an average atom
For example:
35Cl (75.53 % abundance) has atomic mass = 34.97 µ
37Cl (24.47 % abundance) has atomic mass = 36.97 µ
(75.53)(34.97 µ) + (24.47)(36.97 µ)
Atomic mass = ------------------------------------------------- = 35.45 µ
100
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Isotopes and Atomic Weights
Magnesium:
24Mg
(78.991 %); 23.9850 µ
25Mg (10.002 %); 24.9858 µ
26Mg (11.008 %); 25.9826 µ
(78.991%)(23.9850 µ) + (10.002%)(24.9858 µ) + (11.008%); 25.9826 µ
Atomic mass = ------------------------------------------------------------------------------- =
100
Atomic mass of Mg = 24.3052 µ
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Avogadro’s Number: the Mole
Atoms and molecules cannot be counted by
direct observation because of their tiny size.
If we consider a weight of substance that is the same as its formula
(molecular) weight expressed in grams, we have only one number to know:
Avogadro's number, 6.022137 × 1023, usually designated by NA.
The mole (abbreviated mol) is the the SI measure of quantity of a
"chemical entity", which can be an atom,
molecule, formula unit, electron or photon.
One mol of anything is just Avogadro's number of that something.
Or, if you think like a lawyer, you might prefer the official SI definition:
The mole is the amount of substance of a system which contains as many
elementary entities as there are atoms in 0.012 kilogram of carbon 12.
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Avogadro’s Number: the Mole
The Avogadro constant can be applied to any substance.
It corresponds to the number of atoms or molecules
needed to make up a mass equal to the substance's
atomic or molecular mass, in grams.
For example, the atomic mass of iron is 55.847 g/mol,
so NA iron atoms (i.e., one mole of iron atoms) have a
mass of 55.847 g.
Conversely, 55.847 g of iron contains NA iron atoms.
The Avogadro constant also enters into the definition
of the unified atomic mass unit, µ:
1
1
1 µ = ------ = ----------------------- = 1.661 x 10-24 g
NA
6.022 × 1023
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Avogadro’s Number: the Mole
1 mol S atoms =
6.02 x 1023 S atoms
= 32.1 g S
1 mol Cu atoms =
6.02 x 1023 Cu atoms
= 63.5 g Cu
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Avogadro’s Number: the Mole
The mole concept can be applied to molecules instead of atoms.
What is the number of:
a) Moles, and
b) molecules
in 3 oz of table salt, sodium chloride (NaCl)?
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
Avogadro’s Number: the Mole
The mole concept can be applied to molecules instead of atoms.
What is the number of:
a) Moles, and
b) molecules
in 3 oz of table salt, sodium chloride (NaCl)?
Molecular mass (weight) of NaCl is 22.99 + 35.45 = 59.44 µ
1 mole of NaCl = 59.44 g
3 oz NaCl = 3 x 28.35 = 85.05 g
a) 85.05 g of NaCl = 85.05 g/59.44 g = 1.4553 moles of NaCl
b) Number of molecules of NaCl = 1.455 x 6.022x1023 = 8.762x1023
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
The Mole and Chemical Formulas
Chemical formulas represent the numerical relationships
among the atoms in a compound.
2CO2 = 2C + 4O
44.0 g of CO2 contains 12.0 g of C and 32.0 (2x16.0) g of O.
Find the masses of carbon, hydrogen and oxygen in
one mole of ethanol (C2H5OH).
Solution: Using the atomic weights (molar masses) of
these three elements, we have
carbon: (2 mol)(12.0 g mol–1)
= 24.0 g of C
hydrogen: (6 mol)(1.01 g mol–1) = 6.0 g of H
oxygen: (1 mol)(16.0 g mol–1) = 16.0 g of O
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
The Mole and Chemical Formulas
Find the mass fraction and mass percent oxygen in ethanol (C2H5OH).
Solution: Using the information developed in the preceding example, the
molar mass of ethanol is
(24.0 + 6.0+ 16.0)g mol–1 = 46.0 g mol–1.
Of this, 16.0 g is due to oxygen, so its mass fraction in the compound is
(16.0 g)/(46.0 g) = 0.35
which corresponds to 35%.
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
ATOMS and MOLECULES
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic
MATTER
El Camino College
Chemistry 21A
Dr. Dragan Marinkovic