Transcript Atom - RCSD

Atoms, Elements, &
Compounds
Biology II
D. Mitchell
Atom
smallest unit of matter
that cannot be broken
down.
Atomic Structure
• Atoms consist of 3 kinds of subatomic particles:
• electrons- negatively charged subatomic particles
that occupy the outer electron shells
• protons- positively charged subatomic particles
that occupy the nucleus of an atom.
• neutrons- subatomic particles that have no charge
(neutral) and occupy the nucleus of an atom.
Bohr’s Atomic Model
Parts of an atom
ATOMS have a neutral charge
because of its equal number
of positively charged protons
and negatively charged
electrons.
• Different energy levels (electron cloud) can
hold a certain numbers of electrons. Atoms
are most stable when the outermost energy
level is full!
Electron level
1
2
3
4
5
6
# of electrons
2
8
18
32
50
72
(2)Element
•a substance made of one
kind of atom
•can not be broken down
to other substances by
chemical means.
• 91 elements naturally occur
on Earth.
• Life requires about 25
chemical elements.
• Oxygen, Carbon, Hydrogen,
and Nitrogen make up 96%
of the human body’s mass.
Elements in the Human Body
Element
1 Oxygen
2 Carbon
3 Hydrogen H
4 Nitrogen
N
5 Calcium
Symbol
O
C
Element Symbol
6 Phosphorus P
7 Potassium K
8 Sulfur
S
9 Sodium
Ca
* Most abundant to least abundant
Na
Periodic Table of Elements
Lists the following information:
1. Name of element
2. Symbol
3. Atomic number: the number of
protons. (The number of
protons = the number of
electrons.)
4. Atomic mass (Mass Number):
the number of protons plus the
number of neutrons in the
nucleus.
(3) Compound
substance made of two or more elements
bonded together in a fixed ratio.
represented by a chemical formula that
identifies the elements in the compound and
their proportions.
properties are different from the properties
of the elements that make up the compound
Examples
• (1) NaCl -Sodium Chloride
* composed of the elements Sodium(Na) and Chlorine (Cl)
• (2) H2O – Water
*composed of the elements Hydrogen(H) and Oxygen (O)
• (3) C3H6O3 Glucose
*composed of the elements Carbon (C), Hydrogen (H), and
Oxygen (O)
Chemical Bonds
Atoms are the basic building blocks of
matter.
Atoms join with other atoms to form
stable substances.
The attraction between atoms is a
result of their positive or negative
charges.
Atoms join to form compounds and
molecules.
•Electrons determine
whether an atom will bond.
•The number of electrons in
the outermost electron
shell(valence electrons)
determine how many bonds
can be formed.
Oxidation numbers
•indicates the number
of electrons lost,
gained, or shared as
a result of chemical
bonding
What is a chemical bond?
•A chemical bond is formed
when electrons from two
atoms interact and join.
When atoms with incomplete outer
shells interact, they share, receive
(gain), or donate (lose) electrons.
Types of Chemical Bonds
1. Ionic Bond
2. Covalent Bond
3. Hydrogen Bond
Ionic Bonds
• Occur when one atom gains or
loses a valence electron.
• Atoms that lose electrons are
positively charged.
• Atoms that gain electrons are
negatively charged.
• The oppositely charged ions are attracted to each
other.
Characteristics
• Form between metals and
nonmetals
• Ionic compounds tend to form
salts.
• Ionic compounds dissolve easily in
water .
• Ionic compounds easily conduct
electricity.
Covalent Bonds
• A COVALENT BOND results when two
atoms "share" valence electrons
between them.
• This most commonly occurs when
two nonmetals bond together.
• Covalent bonds form molecules (O2 ,
H2) and compounds (CO2)
Hydrogen Bonds
• A hydrogen bond is a bond formed due to a weak
attraction between polar molecules of opposite
charge
• As the name "hydrogen bond" implies, one part of
the bond always involves a hydrogen atom.
• Hydrogen bonds hold the two
strands of the DNA
together.
Why are chemical bonds important?
The type of chemical bond that occurs in a molecule
or substance in part defines its structure,
appearance, and properties.
Example:
NaCl and HCl
Both contain Cl
Table salt and hydrogen chloride