Chemistry
Chapter 1: Chemical Bonds
Vocab
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Electron cloud
Energy levels
Periodic Table
Electron dot diagram
Chemical bond
Atom Structure
• Everything is made up of atoms
• At the center of every atom is a
nucleus containing protons (+ charge)
and neutrons (no charge)
• The nucleus represents most of the atom’s
space
• The rest of the atom’s space is empty
except for the atom’s electrons (- charge)
which travel in an area of space around
the nucleus called the electron cloud
Electrons
• Electrons have negative charges
• Electrons travel in predictable areas
(electron clouds) but not predictable
patterns
Element Structure
• Each element has a different atomic
structure made up of a specific number of
protons, electrons, and neutrons
• The number of protons and electrons is
always the same for a neutral element
Electron Arrangement
• The number and arrangement of electrons
in the electron cloud are responsible for
many of the chemical and physical
properties of that element.
Electron Energy
• All electrons in an atom are in the electron
cloud but some electrons are closer to the
nucleus than others
• Energy levels: The different positions of
electrons in an atom
• Each level represents a different amount
of energy
Number of Electrons
• Each energy level can hold a specific
number of electrons
• The farther away an energy level is from
the nucleus the more electrons it can hold
– Ex. The first can hold 2, the second up to 8,
and the third up to 18 electrons
Second Energy Level
First Energy Level
Energy Steps
• A stairway is an excellent model to show
the maximum number of electrons each
energy level can hold in the electron cloud.
• Electrons nearest the nucleus have the
lowest amounts of energy and are the
hardest to remove
• Electrons farthest from the nucleus have
the most amounts of energy and are the
easiest to remove
Energy Steps
• Ex. Picture a magnet with a chain of
paperclips hanging off of it.
• The easiest paperclip to remove is the one
at the very end of the chain because the
pull of the magnet isn’t as strong
Hardest to remove
Easiest to remove
Periodic Table and Energy Levels
• Periodic Table: A way of representing all
of the elements in a way that shows their
similarities and differences
– First discovered by Dmitri Mendeleev in 1869
– Horizontal rows are called periods
– Vertical columns are called groups or families
– The atomic number is the same as
the number of protons and
electrons
Today’s periodic table is still based on the one I created
almost 140 years ago!
Reading the Periodic Table
Electron Configuration
• The number of electrons in a neutral atom
increases from left to right across a period
• Atoms whose outer energy levels contain
one of the levels in the stair step analogy
are considered stable
• Each period ends with a stable element
Element Families
• Each column of the Periodic Table
contains one family
– Hydrogen is considered separate from the
rest of the families
• Just like human families, element families
have similar traits (chemical properties)
• Mendeleev was inspired by the repeating
patterns he heard in music and saw similar
repeating patterns in the elements
Noble Gases
• Made up of the elements in Group 18
– Helium, Neon, Argon, Krypton, Xenon, Radon
• All are stable and have 8 electrons in their
outer energy levels
• At one time these gases were thought to be
inert (non reactive) but this was later found to
be untrue and the name changed to the
Noble gases
• Used to protect filaments in light bulbs and
produce colored light in signs
Halogens
• Made up of the elements in Group 17
– Fluorine, Chlorine, Bromine, Iodine, Astatine
• Unstable – Halogens need one electron to
obtain a stable outer energy level
– The easier it is for a Halogen to form a bond,
the more reactive it is
• Fluorine is the most reactive because its outer
energy level is closest to the nucleus
• Used to disinfect drinking water, in
clothing bleach, production of paper,
removal of germs during sterilization
and
Alkali Metals
• Made up of the elements in Group 1
– Lithium, Sodium, Potassium, Rubidium,
Caesium, Francium (Hydrogen is not included)
• Unstable - have one electron in their outer
energy level  Highly reactive
• Used to create flavorings and
preservatives and in the manufacturing of
paper, soap, and ceramics
Electron Dot Diagrams
• Electron dot diagram: a diagram that
shows the number of electrons in the outer
energy level
– Valance Electrons: electrons in the outer
energy level
– Helpful in determining the chemical properties
of an atom and when showing how atoms
bond
• Also called Lewis Structures
• Created by Gilbert N. Lewis
How to Write Them
• For groups 1, 2 and 13-18 see pg. 11 in
your book.
• Dots are written in pairs on the four sides
of the element symbol
• The dots are written in this order
1
4
8
5
Ne
3
7
6
2
Using Dot Diagrams
• Can be used to show how atoms bond
with each other
• Chemical Bond: the force that holds two
atoms together
• Atoms bond with each other in a way that
makes them become more stable by filling
up their outer energy levels
Section 2: How Elements
Bond
Vocab
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Ion
Ionic bond
Compound
Covalent bond
Metallic bond
Molecule
Polar bond
Chemical formula
How Elements Bond
• When atoms are joined together they do
not fall apart easily
• Atoms form bonds with other atoms using
the electrons in their outer energy level
• There are 4 ways this can be done:
– Losing electrons
– Gaining electrons
– Pooling electrons
– Sharing electrons
Ionic Bonds – Loss and Gain
• Occurs between metals and nonmetals
• Atoms gain and lose electrons to form
bonds
Ions – A Question of Balance
• Atoms lose or gain electrons and become
more stable
• When an electron is lost, the electric
charge changes because there is now one
more proton than neutron in the nucleus
and it is called a positive ion
• When an electron is gained you create a
negative ion
• Ion: an atom that is no longer neutral
because it has lost or gained an electron
• Examples of ions:
– Sodium loses one electron to become a Na+ ion
– Chlorine gains one electron to become a Cl- ion
Bond Formation
• Negatively charged ions and positively
charged ions are attracted to each other
• Ionic Bond: attraction that holds oppositely
charged ions together
– Ex. Sodium (Na) loses an electron and
becomes a positive ion. Chlorine (Cl) gains an
electron from Sodium (Na) and becomes a
negative ion.
– The two ions are attracted together by an ionic
bond
• Pure substances are divided into two
categories:
– Element: cannot be separated into any
simpler substances
• Ex. Sodium and Chlorine
– Compound: a substance containing two or
more elements that are chemically bonded
• Ex. Sodium Chloride
More Gains and Loses
• Some atoms need to lose/gain more than
two electrons to become stable
• Atoms can do this by bonding to another
atom that needs to gain/lose as many
electrons as they need to lose/gain or by
bonding to more than 1 atom
• Ex:
– Magnesium needs to lose 2 electrons
– Oxygen needs to gain 2 electrons
• The 2 in the superscript represents the number of
electrons that were gained/lost
• If only one electron is gained or lost no number is
needed in the superscript
• Ex:
– Magnesium needs to lose 2 electrons
– 2 Chlorine atoms that each need to gain 1
electron
Metallic Bonding - Pooling
• Occurs between two metals
• Metallic Bonding: Metal atoms pool their
electrons to form bonds
– In metals, electrons are not held tightly to the
individual atoms. Instead they move freely
among all the atoms in the metal forming a
shared pool of electrons
– This is why metal can be hammered into sheets
without breaking and is a good
conductor of electricity
Covalent Bonds - Sharing
• Occurs between 2 nonmetals
• Some atoms need to gain/lose too many
electrons (this needs too much energy) to
create ionic bonds
• Instead two nonmetals share their electrons
• Covalent Bond: chemical bond that forms
between the shared electrons
– Electrons are attracted to the nuclei of both
atoms and move back and forth between them
– Molecule: neutral particle formed in a covalent
bond
– Ex.
• Two chlorine atoms form a stable molecule by
sharing electrons to fill their outer energy level
Double and Triple Bonds
• Sometimes an atom shares more than one
electron with another atom
– When two pairs of electrons are shared it is
called a double bond
– When three pairs of electrons are shared it is
called a triple bond
Polar and Nonpolar Molecules
• While atoms share electrons to become stable
they do not always share electrons equally
– Some atoms have a stronger attraction to
electrons than others
– This unequal sharing makes one side of the
bond more negative than the other
– Polar bond: bond where the electrons are
shared unevenly
• Ex. Water molecules
– Nonpolar bonds: bond where electrons are
shared evenly
The Polar Water Molecule
• 2 hydrogen atoms and 1 oxygen atom
bond together in a covalent bond
• The oxygen has a greater share of the
electrons (sharing one electron with each
hydrogen)
• The oxygen end has a
negative charge
• The hydrogen has a positive
charge
Chemical Shorthand
• In medieval times alchemists were the first
to explore the world of chemistry
– They believed in magic and mythical
transformations
– Discovered many properties of the elements
– Created many symbols to represent the
elements
• Many are still used today
Alchemists, like me, were mainly
concerned with transforming ordinary
metals into gold
Symbols for Atoms
• Modern chemists use symbols to represent
atoms
– These symbols can be understood by chemists
all over the world
– Each element is represented by a one or two
letter symbol
– Many symbols are created by using the common
name of the element
• Ex. H for Hydrogen
– Some symbols are creating by using the name of
the element in another language
• Ex. K for Potassium (which is called Kalium in Latin)
Symbols for Compounds
• Compounds can be described using
element symbols and numbers
– Ex. H2
• This tells us that there are 2 Hydrogen atoms in
this molecule
Chemical Formulas
• Chemical Formula: combination of
chemical symbols and numbers which
shows which elements are present in a
compound
– Ex. Ammonia or NH3
• This tells you that the ratio is one nitrogen atom to
three hydrogen atoms