Atoms - ccmiddleschool

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Transcript Atoms - ccmiddleschool

Atoms – Atomic Structure
Atom Movies:
3-d atomic structure
Atoms, Elements, Compounds
• All matter is made of tiny
particles called atoms
Atoms are the basic
building blocks of all
Elements are the simplest
type of substance
There are 109 (ish)
Atoms of elements
combine to form
compounds (water…)
Atoms and their parts
• Atoms = the smallest part of an element that
still has all the characteristics of that
• About 200 particles smaller than atoms
• 3 main subatomic particles = protons,
neutrons, electrons
Electrons and Energy Levels
• Atoms
• Positively charged
center (nucleus)
• Protons (positive)
• Neutrons (no charge)
• Outside the nucleus are
negative charges
• Electrons
Same # of electrons and
Atomic Number  Protons!
• Number of protons in a nucleus = the
atomic number (look at periodic table,
Hydrogen’s Atomic number = 1)
Atomic Mass
• The atomic mass number of an atom = the
number of protons plus the number of
• Look on periodic table
Periodic Table Songs
• Elements in Order
• Tom Lehrer version –
• First 20 Elements Rap –
Electron Cloud
• Electrons “fly” around
nucleus in energy
• Each level can only
hold so many electrons
• Innermost level holds
2 electrons, second
holds 8(per layer),
third holds 18…
• Electrons in outer
layer = valence
• Protons and neutrons are made of smaller
particles called quarks
Atoms and Bonding
What is Chemical Bonding?
• Combining of atoms to form new
• Rules of chemical bonding are determined
by the structure of atoms
• Negatively charged electrons attracted to
positively charged protons
• This attraction is not strong enough to pull
the electron into the nucleus, but it holds the
atom together
Stable vs. Unstable
• Outermost layer is
“full” (holds
maximum # of
electrons) or complete
• Atom is stable
• Will not form
chemical bonds
• Only “noble” gasses
• Atom with outermost
layer of electrons not
filled will form
chemical bonds
Looking at the Periodic Table of
• Pg 166 and 167
• 18 families of elements (column)
• Elements in same families have common
properties (same # of valence electrons…
• The number in the top corner of each
elements’ box = atomic # (# of protons and
• Element “families” have the same # of
valence electrons!
Electrons and Bonding
• Atoms that do not have their outermost energy
levels filled form bonds
• Some, like Fluorine (F), gains electrons
• Fluorine has 7 valence electrons so it will “gain 1
• Some, like Sodium (Na), lose their electrons
• Sodium has 1 valence electron so it “loses” that 1
Atoms gain or lose electrons to become stable!
(complete outer energy levels)
Ionic Bonding
• Bonding that involves the transfer of
• When electrons are transferred a neutral
atom will become an ion
• Ion = a charged atom
• 1 atom gains electrons and 1 atoms loses
them in an ionic bond
• If an atom gains an electron it becomes
negatively charged
• If an atoms loses an electron it becomes
positively charged
• Let’s draw F + Na…
Energy for Ion Formation
• Ionization is the process of removing
electrons and forming ions
• Ionization energy is the energy needed for
ionization to happen
• Atoms with few valence electrons have low
ionization energy
• The tendency of an atom to attract an
electron is electron affinity
Arrangement of Ions in Ionic
• Ions of opposite charges strongly attract
each other
• Placement of ions in an ionic compound
result in a regular repeating pattern called a
crystal lattice structure
• Gives strength
• Gives shape to crystals of particular compounds
(remember mineral id…)
• Pg 19
Covalent Bonds
• When electrons are not transferred but
shared we have another form of bonding –
covalent bonding
• Electron sharing (co…)
• By sharing electrons each atom fills up its
outer energy level
Nature of Covalent Bonds
• The positively charged nucleus of both
atoms simultaneously attract the negatively
charged electrons being shared
• Simplest covalent bonds is between 2
Hydrogen atoms
• PG 22
Electron Dot Diagram
• Chemists use these
drawings to show
electron sharing that
happens in covalent
• The element symbol
represents the nucleus
and all the inner
energy levels
• The dots represent the
valence electrons
Let’s draw a few more
Pg 22
Diatomic Elements
• Covalent bonds often happened between
atoms of the same elements
• Hydrogen, chlorine, fluorine, bromine,
iodine, nitrogen
Molecule Formation
• The combination of atoms from covalent
bonds form molecules rather than crystal
lattice structures
• A molecule is the smallest particle of a
covalently bonded substance
• Molecules are represented by chemical
• HCL – 1 Hydrogen and 1 Chlorine
(hydrochloric acid)
Water Molecule
Chemical Formula
Polyatomic Ions
• Covalently bonded atoms that tend to stay
together and act like a single atom when
they combine with other atoms
• Polyatomic ions have covalent bonds, but
when they bond with other atoms they
usually form ionic bonds
• Pg 24
• The polyatomic Ion hydrogen carbonate
bonds with sodium to produce sodium
hydrogen carbonate = Baking Soda!
Metallic Bonds
• Metals are elements that give up electrons
easily (copper, silver, gold, iron, tin, zinc,
nickel, chromium…)
• Metallic solids = solids made entirely of 1
metallic element
• Metallic bonds – outer electrons of the
atoms form a common electron cloud
Sea of Electrons
• Electrons become the property of all the
atoms bonded
• The positive nuclei of the atoms are
surrounded by free-moving electrons that
are attracted by the nuclei
Properties of metals
• Malleable – hammered into thin sheets
• Ductile – drawn into wire
• Flexibility – metal ions can slide past each
other and electrons free-flow, yet the
positive and negative attractions hold the
metal together
• Conduct heat and electricity
• High melting points
Predicting Types of Bonds
• Elements at the left and center of the
periodic table are metals – form metallic
bonds with each other
• Elements at the right gain electrons easily
• Bonds between metals and nonmetals =
• Bonds between nonmetals = covalent
Combining Capacity of Atoms
• Oxidation Number = the # of electrons an
atom gains, loses, or shares when it forms a
Oxidation # describes combining capacity
Sodium’s oxidation number = 1+
Magnesium = 2+
Chlorine = 1-
Using Oxidation Numbers
• We use oxidation
numbers to predict
how an atom will
combine (or not) and
to determine chemical
• Na 1+ plus Cl 1- =
• Mg 2+ plus Cl 1- =