Download Atomic Structure and Periodic Table Unit Notes Elements

Atomic Structure and Periodic Table Unit Notes
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Elements- An element is either classified as a metal, nonmetal, or metalloid. The classification
depends on the element’s location on the periodic table.
Properties of Metals:
o Metals are elements that have luster, conduct heat and electricity, and usually bend without
breaking. Metals are also ductile (can be drawn out into a wire).
o All metals except mercury (Hg) are solids at room temperature; in fact, most have extremely
high melting points and high boiling points.
o A metal’s reactivity is its ability to react with another substance. Metals in the first and
second column of the periodic table are more reactive than other metals.
Properties of Nonmetals:
o Although the majority of the elements in the periodic table are metals, many nonmetals are
abundant in nature.
o Most nonmetals don’t conduct electricity, are much poorer conductors of heat than metals,
and are brittle when solid.
o Many are gases at room temperature; those that are solids lack the luster of metals.
o Their melting points tend to be lower than those of metals.
o Fluorine is the most reactive nonmetal.
Properties of Metalloids
o Metalloids have some chemical and physical properties of metals and other properties of
nonmetals. In the periodic table, the metalloids lie along the border between metals and
nonmetals.
o Some metalloids such as silicon (Si), germanium (Ge), and arsenic (As) are semiconductors.
A semiconductor is an element that does not conduct electricity as well as a metal, but does
conduct slightly better than a nonmetal.
Properties of Metals and Nonmetals
Metals
Nonmetals
Bright metallic luster
Non-lustrous, various colors
Solids are easily deformed
Solids may be hard or soft, usually brittle
Good conductors of heat and electricity
Poor conductors of heat and electricity
Loosely held valence electrons
Tightly held valence electrons
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Modern View of the Atom
o The atom has two regions and is 3-dimensional.
 The nucleus is at the center and contains the protons and neutrons.
 The electron cloud is the region where you might find an electron and most of the
volume of an atom.
Subatomic Particles
Name
Electron
Proton
Neutron
Symbol
ep+
n0
Charge
-1
+1
0
Relative Mass
1/2000 amu
1 amu
1 amu
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Atomic number
o The atomic number of an element is the number of protons in the nucleus of an atom of
that element.
o The number of protons determines the identity of an element, as well as many of its
chemical and physical properties.
Mass Number
o The sum of protons and neutrons in the nucleus is the mass number of that particular atom.
Symbols
o Elements can be represented by using the symbol of the element, the mass number and the
atomic number.
o The mass number is the atomic mass rounded to a whole number.
𝐴 𝑛
𝑍𝑋
A = mass number
Symbol
Protons
Z = atomic number
Neutrons
Electrons
n = charge
Atomic Number
Mass Number
34
78
19
9𝐹
80
35𝐵𝑟
91
140
35 −1
17𝐶 𝑙
27 +3
13𝐴𝑙
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Cations
o A cation is a positive ion.
o It is formed when an atom loses one or more electrons.
Anions
o An anion is a negative ion.
o It is formed when an atom gains one or more electrons.
Isotopes
o In 1910, J.J. Thomson discovered that neon consisted of atoms of two different masses.
o Atoms of an element that are chemically alike but differ in mass are called isotopes of the
element.
o Consider the isotope of carbon that has a mass number of 14. The following are different
ways to write symbols for this isotope.
Carbon-14
C-14
14
𝐶
14
6𝐶
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The Bohr Model of the Atom
o Niels Bohr, a young Danish physicist working in Rutherford’s laboratory in 1913, suggested
that the single electron in a hydrogen atom moves around the nucleus in only certain
allowed circular orbits.
o The atom looked like a miniature solar system. The nucleus is represented by the sun, and
the electrons act like the planets.
o The orbits are circular and are at different levels. Amounts of energy separate one level
from another.
Bohr Diagrams
o Find your element on the periodic table.
o Determine the number of electrons.
o This is how many electrons you will draw.
o Find out which period (row) your element is in.
 Elements in the 1st period have one energy level.
 Elements in the 2nd period have two energy levels, and so on.
o Draw a nucleus with the element symbol inside.
o Draw the shells around the nucleus.
o Add the electrons.
 The first shell can only hold 2 electrons.
 The second can only hold 8 electrons.
 The third shell can only hold 18 electrons.
Electron Dot Diagrams
o An electron dot diagram illustrates valence electrons as dots (or other small symbols)
around the chemical symbol of an element.
o Each dot represents one valence electron.
o In the dot diagram, the element’s symbol represents the core of the atom—the nucleus plus
all the inner electrons.
o Write the symbol.
o Put one dot for each valence electron.
o Don’t pair electrons up until you have to.
Bonding and Molecules
o The outer electrons are involved in bonding. These are called valence electrons.
o Most stable atoms have eight valence electrons. When an atom has 8 valence electrons, it
is said to have an octet of electrons.
Oxidation Number
o An oxidation number indicates how many electrons are lost, gained, or shared when
bonding occurs.
The elements in the A groups are called the representative elements.
1A
o Group 1A element have one valence electrons.
o They form +1 ions after losing the one valence electron. 1+ is referred to as the oxidation
number for Group 1A elements.
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2A
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Group 2A elements have two valence electrons.
They form +2 ions after losing the 2 valence electrons. 2+ is referred to as the oxidation
number for group 2A elements.
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Group 3A element have three valence electrons.
They form +3 ions after losing the 3 valence electrons. 3+ is referred to as the oxidation
number for Group 3A elements.
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Group 4A elements have four valence electrons.
They form +4 ions after losing the 4 valence electrons. They could just as easily form -4 ions
after gaining four electrons.
Group 4A elements could have a 4+ or 4- oxidation number, depending on the element with
which they are bonding.
Two elements in Group 4A have multiple oxidation numbers of 2+ and 4+. These two
elements are tin (Sn) and lead (Pb).
3A
4A
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5A
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Group 5A elements have five valence electrons.
They form 3- ions after gaining additional electrons. 3- is referred to as the oxidation
number for Group 5A elements.
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Group 6A elements have six valence electrons.
They form -2 ions after gaining additional electrons. 2- is referred to as the oxidation
number for Group 6A elements.
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Group 7A elements have seven valence electrons.
They form -1 ions after gaining 1 additional electron. 1- is referred to as the oxidation
number for Group 7A elements.
6A
7A
8A
o Group 8A elements have eight valence electrons, except helium which only has 2.
o Group 8A elements, with a full complement of valence electrons, are generally not reactive.
Reactivity of Metals
o In general, the reactivity of metals increases from top to bottom and decreases from left to
right.
Reactivity of Nonmetals
o In general, the reactivity of nonmetals increases from left to right and decreases from top to
bottom.