Download Atoms & Elements

What is matter ?
Matter is the “stuff” that
makes up all things.
Composed
 pure substances
 mixtures
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Let’s look at pure substances?
• matter with a specific composition.
• an element when composed of one type of atom.
Elements are
• pure substances that contains atoms of only one type.
• Copper, Cu, Lead, Pb, Aluminum, Al
• compound when composed of two or more elements
combined in definite ratio
• contain two or more elements in definite ratio
Salt (NaCl)
Table sugar (C12H22O11)
Water (H2O)
Table salt:
elements sodium and chlorine
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What are mixtures?
type of matter:
• two or more substances that are physically mixed, not
chemically combined.
• two or more substances in different proportions.
substances that can be separated by physical methods.
homogeneous mixture
uniform composition
heterogeneous mixture,
not uniform.
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What are elements?
Elements are
• pure substances that cannot be separated into
•
simpler substances by ordinary laboratory
processes.
the building blocks of matter.
Some elements are
named for planets,
mythological figures,
minerals, colors,
scientists, and
places.
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Symbols of Elements
A symbol
• represents the name of an element.
• consists of 1 or 2 letters.
• starts with a capital letter.
• Symbols from Latin Names
• Cu, copper (cuprum) , Fe, iron (ferrum)
1-Letter Symbols
C carbon
N nitrogen
F fluorine
O oxygen
, Au, gold (aurum)
2-Letter Symbols
Co cobalt
Ca calcium
Al aluminum
Mg magnesium
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What are physical properties of
elements?
The physical properties of an element
• are observed or measured without changing its
identity.
• include the following:
Shape
Density
Color
Melting point
Odor and taste
Boiling Point
What is a Periodic table?
On the periodic table,
• elements are arranged according to similar
properties.
• groups contain elements with similar properties in
vertical columns.
• periods are horizontal rows of elements.
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What are group numbers?
Group Numbers
• letter A for representative
elements (1A to 8A)
• letter B for transition
elements.
• Several groups of representative
elements
have common names.
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Metals, Nonmetals, and Metalloids
heavy zigzag line
separates metals and
nonmetals.
• Metals located to left.
• Nonmetals located to right.
• Metalloids are located
between metals and
nonmetals.
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Properties of Metals, Nonmetals, and
Metalloids
Metals
• are shiny and ductile.
• are good conductors of heat and electricity.
Nonmetals
• are dull, brittle, and poor conductors.
• are good insulators.
Metalloids
• are better conductors than nonmetals, but not
as good as metals.
• are used as semiconductors and insulators.
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What is matter composed of?
In Dalton’s Atomic Theory, atoms
• are tiny particles of matter.
• of an element are similar and
•
•
different from other elements.
of two or more different elements
combine to form compounds.
are rearranged to form new
combinations in a chemical
reaction.
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Subatomic Particles
Atoms contains subatomic particles,
• protons have a positive (+) charge.
• electrons have a negative (-) charge.
• like charges repel and unlike charges
•
attract.
neutrons are neutral.
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Rutherford’s Gold-Foil Experiment
In Rutherford’s gold-foil experiment, positively
charged particles
•
were aimed at atoms of gold.
•
mostly went straight through the atoms.
•
were deflected only occasionally.
Conclusion:
There must be a small, dense, positively charged nucleus
in the atom that deflects positive particles that come close.
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Structure of atom:
An atom consists
• of a nucleus that contains protons and
neutrons.
• of electrons in a large empty space
around the nucleus.
• a proton has a mass of about 1 (1.007) amu.
• a neutron has a mass of about 1 (1.008) amu.
• an electron has a very small mass, 0.000549 amu.
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What is atomic number?
The atomic number
• is specific for each element.
• is the same for all atoms of an element.
• is equal to the number of protons in an atom.
• appears above the symbol of an element.
Atomic Number
Symbol
11
Na
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Atomic Number and Protons
• Hydrogen has atomic
number 1; every H atom
has one proton.
• Carbon has atomic
number 6; every C atom
has six protons.
• Copper has atomic
number 29; every Cu atom
has 29 protons.
• Gold has atomic number
79; every Au atom has 79
protons.
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Electrons in An Atom
An atom of
• an element is electrically neutral; net charge of an
atom is zero.
• has an equal number of protons and electrons.
number of protons = number of electrons
Aluminum has 13 protons and 13 electrons. The net
charge is zero.
13 protons (13+) + 13 electrons (13 -) = 0
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What is mass number?
The mass number
• Represents number of particles in the nucleus.
• equal to number of protons + number of neutrons
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Let’s look at isotopes!
Isotopes
• are atoms of same element that have different mass
numbers.
• have same number of protons, but different
numbers of neutrons.
24Mg
25Mg
26Mg
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12
12
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Isotopes of Sulfur
A sample of naturally
occurring sulfur contains
several isotopes with the
following abundances
Isotope % abundance
32S
95.02
33S
0.75
34S
4.21
36S
0.02
32S, 33S, 34S, 36S
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16
16
16
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What is atomic mass?
Na
22.99
The atomic mass of an element
• listed below symbol of each element on
periodic table
• Gives mass of an “average” atom of each
element compared to 12C.
• is not same as mass number
The atomic mass of chlorine is
• due to all Cl isotopes.
• not a whole number.
• average of two isotopes: 35Cl and 37Cl.
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What is a nuclear symbol?
A nuclear symbol
• represents a particular atom of an element.
• gives mass number in upper left corner and atomic
number in lower left corner.
Example: An atom of sodium with atomic number
11 and a mass number 23 has the following atomic
symbol:
mass number
23
Na
atomic number
11
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Information from Nuclear Symbols
From nuclear symbol, we can determine number of
protons (p+), neutrons, (n), and electrons (e-) in a
particular atom.
16
8
31
O
8 p+
8n
8 e-
15
65
P
15 p+
16 n
15 e-
Zn
30
30 p+
35 n
30 e-
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How electrons are arranged!
Energy levels
• are assigned numbers n = 1, 2, 3, 4 and so on.
• increase in energy as value of n increases.
• are like rungs of a ladder with lower energy
levels nearer the ground.
Energy levels have a maximum number of
electrons equal to 2n2.
Energy level
Maximum number of
electrons
n=1
2(1)2 = 2(1) = 2
n=2
2(2)2 = 2(4) = 8
n=3
2(3)2 = 2(9) = 18
n=4
n=3
n=2
n=1
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What are valence electrons?
valence electrons :elements in group have same
number of outer shell electrons
• determine chemical properties of the elements.
• are electrons in highest energy level.
• are related to group number of the element.
Example: Elements in group 2A(2) have two (2)
valence electrons.
Be
2, 2
Mg 2, 8, 2
Ca
2, 8, 8, 2
Sr
2, 8, 18, 8, 2
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Periodic Table and Valence Electrons
trend!
Representative Elements Group Numbers
1
2
3
4
5
6
7
H
1
Li
2,1
Be
2,2
Al
2,3
C
2,4
N
2,5
O
2,6
8
He
2
F
Ne
2,7 2,8
Li
Mg
Ge Si
P
S
Cl
Ar
2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8
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Electron-Dot Symbols
An electron-dot symbol
• shows valence electrons
around symbol of element.
• for Mg has two valence
electrons as single dots on
sides of symbol Mg.
.
.
·Mg · or Mg · or ·Mg or ·Mg
·
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Writing Electron-Dot Symbols
Electron-dot symbols for
• groups 1A(1) to 4A(14) use single dots.
·
·
Na ·
· Mg ·
· Al ·
·C·
·
• groups 5A(15) to 7A(17) use pairs and single dots.
··
·P·
·
··
:O·
·
In a group, all electron-dot symbols have
same number of valence electrons
Atomic Size
Atomic size is described using atomic radius; distance
from nucleus to valence electrons.
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Atomic Radius Within A Group
Atomic radius increases
going down each group
of representative
elements.
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Atomic Radius Across a Period
Going across a period left to right,
• an increase in number of protons increases attraction for
valence electrons.
• atomic radius decreases.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Ionization Energy
Ionization energy: energy takes to remove a valence electron.
going up a group of representative elements,
• distance decreases between nucleus and valence electrons.
• ionization energy increases.
Na(g) + Energy (ionization)  Na+(g) + e-
•Metals have lower ionization energies.
•Nonmetals have higher ionization
energies.
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