Transcript Chemistry Intro Ch 2

A. Chemistry =
study of the composition,
structure, properties, and
reactions of a substance.
• Life depends on chemistry . . .
Because chemical compounds
are the building blocks of life.
NOTE: MASS=
Mass vs.
weight
animation
The quantity of matter an object has.
MASS AND WEIGHT ARE NOT THE SAME!
1. Definition= basic unit of matter
2. Atoms are composed
protons(+), neutrons(0), and
electrons(-)
3. Protons and neutrons are
located in a central area called the
nucleus.
4. Electrons move about the nucleus.
The # of electrons is equal to the # of
protons.
1. Definition = a pure substance that
contains only one type of atom
2. About 96% of the mass of all kinds of living things is
composed of a combination of just 4 elements…
Image from: http://www.sciencelearn.org.nz/Contexts/Just-Elemental/Sci-Media/Images/Elements-in-the-human-body
3. Periodic Table—developed as a way
to organize elements
Trends in periodic table
 Elements are found in order of atomic number (#
of protons)
Atomic weight (# of protons + # of neutrons) get
bigger as you go across and down
Periods of elements = rows
---As you go across a row, elements get
smaller in size BUT greater in mass
---Example: The go from a beach ball to a
bowling ball
 Groups of elements = columns
Elements in the same group have similar properties
and will bond in similar ways
GROUPS/FAMILIES
As you go L to R across a period
PERIODIC TABLE
Atomic size
decreases and
atomic mass
increases
Information gathered from the
PERIODIC TABLE
2
He
Helium
4
***Element Song***
Atomic Number
Chemical Symbol
Element Name
Atomic Mass
**Harry Potter Elements Song**
2. Remember mass number = number of
protons plus neutrons in nucleus of atom
Example: carbon-12, carbon-13, carbon-14
Carbon – 12
# protons
# neutrons
Carbon – 13
Carbon – 14
Go to element exploration . . .
MOST elements do not exist by themselves. . . . .
1. Definition: a substance formed by the
bonding of two or more elements in definite
proportions
2. Chemical formula = shows the
composition of the compound

Examples: H2O, NaCl, CO2
3. physical and chemical properties of compound
are DIFFERENT from each element alone
G. Bohr Models of Atoms
1st electron shell can hold—2 electrons
2nd electron shell can hold—8 electrons
3rd electron shell can hold—8 electrons
Examples: Hydrogen (1)
Oxygen (8)
Carbon (6)
Chlorine (17)
1. Definition= the forces that hold together
the atoms that make up compounds
2. Two main types of STRONG chemical bonds:
1= ionic bonds
2= covalent bonds
. . . Let’s take a look at each type
more closely . . . .
1. Ionic bonds
---a TRANSFER of
electrons takes
place resulting in
ions
---ion = a positively
or negatively
charged atom
---ions of opposite
charge attract
strongly, thus
forming an ionic
bond
Example: NaCl
The number of electrons in outer energy shell
determines the chemical properties of an atom.
**Atoms want their outermost shell to be full**
When sodium chloride (NaCl) is formed, one
electron from sodium is transferred to chlorine.
**Ionic Demo**
2. Covalent bonds
---involves SHARING of electrons
---single covalent bond = share one
electron
---double covalent bond = share two
electrons . . .etc.
--result of covalent bond = a
molecule . . . which is the smallest
unit of a compound
--Example: Methane (CH4)
**Covalent Demo**
click through tutorial reading 1-14, 22-24, and 30
In a double bond,
2 atoms share 2 pairs of electrons (4 electrons)
In a triple bond,
2 atoms share 3 pairs of electrons (6 electrons)
Sharing of electrons
between two
Oxygen atoms
Structure of the 4 elements that make up most of
the mass of living things: