Transcript Atoms and Molecules - Sonoma Valley High School

Atoms and Molecules
Macromolecule –a Protein
Caffeine molecule
Atomic structure
• Small, dense nucleus
– Protons: (+) charge
– Neutrons : (0) no charge
• Electrons (-) found in orbitals
of different energy levels
around the nucleus.
• # Protons = # electrons
• Electrically neutral, as + and
– charges are equal
Energy levels
• Electrons fill up
orbitals around the
nucleus from the
inside out.
• Each level holds only
so many electrons
• Level 1- holds 2
• Level 2 – holds 8
• Level 3- holds 8
Valence electrons
•the electrons on the outermost level are called valence
electrons, and they determine reactivity
•Reactivity is how likely an atom is to form bonds with
another element
Think: How
many
valence
electrons
does Ar
have? and
H?
Elements
• Every element has a
unique number of
protons.
– It is the number of
protons that defines
what the element is.
– The atomic number is
the number of protons
– The atomic mass is the
number of protons plus
neutrons
Lithium: Atomic # = 3, Atomic
mass = 6
The periodic table
• The periodic table is a tool that organizes elements
– Groups (columns). of elements have the same number of valence
electrons
– Periods (rows) of elements have the same number of energy levels.
What is a chemical bond?
Attractive forces that hold atoms and ions
together, making molecules
• An ionic bond holds ions together
• A covalent bond holds atoms together
Types of bonds
Water: two hydrogen atoms
plus an oxygen atom.
• Covalent bonds
– Two or more atoms share
electrons.
– Example: water
• Ionic bonds
– Formed when electrons are
transferred.
– Atoms become charged (ions)
– Opposite charged ions attract
each other.
– Example: salt
Salt: one chlorine atom
plus one sodium atom.
Compounds
• Molecules
composed of atoms
of two or more
elements.
• Held together by
chemical bonds.
– Chemical bonds require
energy to form.
– Chemical bonds result
from outer electrons
(valence electrons)
interacting.
Methane gas molecule CH4
Think: How many atoms are in
methane? How many elements are
in methane?
Polarity
• Elections are either
shared equally or not
between atoms in a
compounds
• Polar: When electrons
are not shared equally,
one end of the molecule
is more positive and the
other more negative.
• Nonpolar: an even
distribution of charge
Summary: answer the following as a 7
sentence paragraph
1.
2.
3.
4.
5.
6.
What is the basic structure of an atom?
What is an element?
Why do elements form bonds?
What type of bonds do elements form?
What is a compound?
What is polarity?