Transcript PowerPoint Nature of Atoms

Nature of molecules
and Properties of
Water
Democritus – 450 B.C. – “Cannot Be Cut”
Nature of Atoms
Matter- occupies space and has mass
 ATOMS
Central Nucleus: Protons- positive charge and Neutrons- neutral
charge
Electrons- negative charge - surround the nucleus –electron cloud
*electrons held in place by positively charged protons

How Do You Know the Number of
Protons?
 Atomic
Number – Carbon is 6, Oxygen is 8.
 Typically,
an atom has equal number of
electrons- neutral- charges balance out
 Chemical
electrons

Behavior is determined by
How Heavy is an Atom?
 Atomic
Mass: Sum of the masses of
the protons and neutrons
 Measured in daltons – take 602 million
million billion (6.02 X 10 23) to make 1
gram (g).
 Electrons weigh 1/1840 of a dalton
Isotopes

Vary in number of neutrons. The atomic mass is
the protons + the average number of nuetrons
found in nature

Carbon ----Carbon 12 – has 6 protons and ?
Neutrons
Carbon 13- has 6 protons and ? Neutrons
Carbon 14- has 6 protons and ?
Neutrons
The atomic mass of carbon is
Radioactive isotopes (unstable)- used in dating
fossils, rocks, etc- also used in medicine (tracers) -
ELECTRONS

Determine the chemical behavior of atoms

Found in orbitals around the nucleus

Atoms contain energy levels –

The outer electrons (valence) are available to
react with other atoms to form compounds or
molecules
ELEMENTS IN LIVING
SYSTEMS

90 elements of the 118 occur naturally

Of the 90 naturally occurring elements on Earth, only 12 are found in
living systems in more than trace amounts – (C, H, O, N, P, S, Na, K,
Ca, Mg, Fe, Cl).

Carbon, Hydrogen, Oxygen, and Nitrogen (96.3% weight of the human
body)

Dmitri Mendeleev – 19th century – Russian chemist- came up with one
of the great generalizations – elements repeats itself in groups of
eight.

Repeats in the outermost shell- valence electrons (octet rule)
TRACE ELEMENTS

Iodine

Zinc

Manganese

Copper
ELECTRON ENERGY LEVELS
 First
energy level/shell- 2 electrons
 Second
 Third
energy level/shell- 8 electrons
energy level/shell-8 electrons
 Stable
elements have 8 electrons in their
outer shell.
Bohr Model – Practice
Hydrogen (H)
Carbon (C)
Calcium (Ca)
Sodium (Na)
Neon (Ne)
Argon (Ar
Chlorine (Cl)
Carbon
Hydrogen
Sodium
Neon
Calcium
Stability of Atoms

Mendeleev – octet rule- need 8 electrons for a stable atom.

How many to make hydrogen stable?
carbon stable?

How many to make calcium stable?
sodium stable

How many to make Neon stable?

How many to make chlorine stable?

Look at the Bohr models- Which atoms are likely to gain electrons?
Which are likely to give electrons away? Think about energy (work
required)
Argon stable?
Elements, Compounds and Molecules

Elements- composed of only one type of atom.

The element of carbons contains only

Molecule - smallest fundamental unit of a chemical
compound that can take part in a chemical reaction.

Compound – mixture of two or more atoms (elements)

Chemical bonds- atoms of molecules join together

Covalent bonds; Sharing of electrons (two non-metals)

Ionic bonds: bonding between ions- transfer or receive
electrons (metal and a nonmetal
atoms.
Practice Bonding

Gumdrops

Molecule
Type of Bond

H2
Covalent
Gumdrop Model
Dot Structure
Bonding
Sodium
Chloride

Molecule
NaCl
Type of bond
ionic – metal/non
Gumdrop Model
Dot Model
WATER
– H2O

MOLECULE
TYPE OF BOND

H2O
COVALENT
GUMDROP MODEL
DOT STRUCTURE
Do More
Na20
(2 sodium and one oxygen)
CaCl2 (1 calcium and 2 chlorine)
CH4 (1 carbon and 4 hydrogen)
CO2 (1 carbon and 2 oxygen)
WATER AND POLARITY

Covalent bond-

See video –

https://www.youtube.com/watch?v=HVT3Y3_gHGg (water)- Crash Course

Amoeba Sister-

https://www.youtube.com/watch?v=3jwAGWky98c
WATER, WATER EVERYWHERE

Because water is a polar covalent bond it has
amazing characteristics

1. Cohesion –attraction of two like molecules –
leaves pull water up from the roots, seeds swell
and germinate, surface tension – gives high heat
capacity

2. specific heat- do not change temperature
easily- Water stabilizes temperature of organisms
and the environment

3. Lower density of ice – water molecules are
spaced apart when frozen- lakes freeze top down.
Protects life in water