Atoms and Molecules
 What
do the letters in the box
mean?
 Can you name any of them?
 An element is a substance that
can’t be broken down into
simpler chemical substance
 92 elements occur naturally
 The rest are man-made
CHNOPS make up 98% of body
Table 6.1 Some Elements That Make Up the Human Body
Percent By
Percent By
Element
Element
Symbol Mass in
Symbol Mass in
Human Body
Human Body
Oxygen
Fe
O
65.0
Iron
trace
Zn
Zinc
Carbon
C
18.5
trace
Hydrogen
Cu
H
9.5
Copper
trace
I
Iodine
Nitrogen
N
3.3
trace
Calcium
Ca
1.5
trace
Manganese Mn
Boron
B
1.0
Phosphorus P
trace
Cr
K
Potassium
0.4
Chromium
trace
trace
Molybdenum Mo
Sulfur
S
0.3
Cobalt
Sodium
Co
trace
Na
0.2
Se
Chlorine
0.2
Selenium
trace
Cl
Fluorine
F
Magnesium Mg
0.1
trace
The Periodic Table
 Periodic
Law – states that the
properties of the elements
repeat periodically if the
elements are arranged in order
of increasing atomic number
 Organizational tool
 Groups
(families)– vertical
columns
–Elements in same group
behave similarly due to
structure
 Periods – horizontal rows
 Regions
 Left – Metals
 Right – Nonmetals
 Between – Staircase of
metalloids or semi-metals
Break Down
 Atoms
– building blocks of
matter
-----
 Elements – purest substance
 Molecule – group of atoms
bonded to form new substance
 Compound – 2 or more different
elements in fixed ratios
Two Elements
Molecules
Structure of Atoms
 Three
fundamental units of an
atom are the
 Proton – positive charge
 Neutron – neutral charge
 Nucleus – center of atom,
location of proton and neutron
 Electron – negative charge
Dalton’s Atomic Theory
 1.
All elements are made of
atoms, which are indivisible and
indestructible particles.
 2.
All atoms of the same
element are exactly alike - they
have the same mass.
 3.
Atoms of different elements
are different – they have
different masses.
 4. Compounds are formed by
the joining of atoms of 2 or more
elements. In any compound, the
atoms of the different elements
are joined in a definite, wholenumber ratio, such as 1:1, 2:1,
or 3:2
Modern View
 1.
Atoms are NOT indivisible – they
can be broken apart into P+,
neutrons, and e-.
 2. Atoms can be changed from one
element to another, but not by
chemical means (chemical
reactions). Can do it by nuclear
reactions.
 3. Atoms of the same element are
NOT all exactly alike  isotopes
Numbers on Periodic Table
 Atomic
number (Z) - number of
protons
 Each atom has a different atomic
number
 Mass number (A) – number of
protons + neutrons
 Number of neutrons can change
Isotopes
 Atoms
of the same element that
differ in the number of neutrons
 Carbon has how many protons?
 Most carbons have 6 neutrons
 Atomic number = ?
 Some carbons have 8 neutrons
 Atomic number = ?
Ions
A
charged atom due to an
unequal number of protons and
electrons
 Cation = positive ion
 Anion = negative ion
 Wants to be neutral -> bonding
Models of the Atom
Charge of an Atom
 Atoms
want to be neutral overall
 Electrons have a negative charge
 Protons have a positive charge
 Atoms tend to gain or lose their
outer electrons
 Try to have outer valence shell
filled
 First
level can hold two electrons
 The rest hold eight
 This is the Noble Gas
configuration
 Amount they gain or lose
determine type and number of
bonds
Ionic Bonds
 Atoms
become ions by gaining or
losing their electrons
 Oppositely charged ions are
attracted to each other
 Tend to form between Group I
and VIIa
 Relatively weak and
disassociates easily in water
Covalent Bonds
 Forms
when atoms share
electrons
 Electron-sharing bond
 Electrons can move very fast so
can fill both outer shells
Polar Covalent Bond
 Uneven
sharing of bonds
 Electrons spend more time with
the more non-metallic one
 One atom will be more negative
 One atom will be more positive
 Example: Water molecule
Water Molecule
 Electrons
spend more time with
O2 (greater electronegativity)
 That end becomes slightly
negative
 The other becomes slightly
positive as a result
 This is a polar molecule