Transcript Atoms Water and pH Pre

Protons, Electrons, and
Neutrons
Protons, Electrons, and
Neutrons
Charges:
 Electrons - Negatively charged
 Protons - Positively charged
 Neutrons – Neutral (no charge)
Element Name
Beryllium
Atomic Number
4
(# protons)
(# of protons
and electrons)
Be
Element Symbol
Atomic Mass
9.01
(# protons + # neutrons)
protons)
Mass Number - Atomic Number = # of neutrons
+
+
++
9-
4
=
5
What are the numbers of protons, electrons and neutrons?
Chlorine
17
Cl
35.45
Protons =
17
PElectrons
= 17
= 17
E = 17
= 18
NNeutrons
= 19
Where are protons, electrons,
and neutrons located?
Protons –inside the
atomic nucleus
Neutrons –inside the
atomic nucleus
Electrons –orbit the
atomic nucleus
Electrons
Protons and
Neutrons
Isotopes

Different atoms of the same element


# Protons stays the same
# Neutrons are different
Ex. Carbon 12 – 6P, 6N, 6E
Carbon 13 – 6P, 7N, 6E
Carbon 14 – 6P, 8N, 6E
The have the same # electrons
The chemical properties don’t change
Chemical Bonds
1.
Ionic Bonds –formed b/w
oppositely charged ions

An atom that loses
electrons has a +
charge

An atom that gains
electrons has a –
charge

Ions- Positively and
negatively charged
atoms
2. Covalent Bonds- electrons
are shared b/w atoms
 When atoms share 2
electrons => single
covalent bond
 When atoms share 4
electrons => double
covalent bond
Water and pH
Water
 Covers
3/4 of Earth's surface
 The single most abundant compound in
most living things
 One of the few compounds that is a liquid
at the temperatures found on the Earth's
surface
Density of Water
Unlike most substances,
water expands as it freezes



Ice is less dense than liquid
water and therefore floats
If ice sank it would be
disastrous for:
1. fish and plant life in regions w/
cold winters
2. sport of ice skating
Polarity: The Water Molecule
 Water

is a polar molecule
Due to the unequal sharing
of electrons
• The oxygen end has a slight (-)
charge
• The hydrogen end has a slight
(+) charge
• http://programs.northlandcollege.
edu/biology/Biology1111/animati
ons/hydrogenbonds.html
+
Hydrogen Bonds

Polar molecules, such as H20, attract each other
because of their partial (+) and partial (-) charges
 This is a hydrogen bond
 Not as strong as covalent or ionic bonds

Because it is only b/w partial charges
Properties of Water
 The
ability of water to form multiple
hydrogen bonds is responsible for many of
water's properties

One water molecule may be involved in 4
hydrogen bonds at the same time
Properties of Water
Cohesion- an attraction b/w molecules
of the same substance
1.


Why drops of water form beads on a smooth
surface
Also explains why some insects and spiders
can walk on a pond's surface
•
AKA “Surface Tension”
Properties of Water (Cont’d)
2. Adhesion- an attraction b/w molecules of
different substances

The meniscus in a graduated cylinder
• Forms because adhesion b/w water molecules and
glass molecules is stronger than the cohesion
between water molecules

Capillary Action
• Adhesion also causes water to rise in a narrow
tube against the force of gravity
• One of the forces that draw water out of the roots
of a plant and up into its stems and leaves
Mixtures
 Mixture-
a material composed of 2+
elements or compounds that are physically
mixed together but not chemically
combined


Examples - Salt & pepper or a Salad
Cookies and Cream Ice Cream
Solutions
 Solution
- Mixture of 2+ substances where
the molecules of the substances are
evenly distributed


Solute - substance that is dissolved (ex. salt)
Solvent - substance in which the solute
dissolves (ex. water)
**Water is the
universal solvent
because of its
polarity
pH Scale


A water molecule can react to form ions
The pH scale is used to indicate the
concentration of H+ ions in solution
 pH stands for “power of Hydrogen”
If more H+ than OH-, the chemical is an ACID
H+
H
O OHIf less H+ than OH-, the chemical is a BASE
H+
H
O OHIf equal amounts of H+ and OH-, the chemical is NEUTRAL
H+
H
O OH-
10
11
12
13
14
More Acidic H+
1
2
3
4
5
6
7
8
9
Neutral
More Basic OH-
0
An acid with a pH of 1 is
stronger than one with a
pH of 6
• Litmus paper is used as an indicator
for acids and bases
Acids turn blue litmus  to red
Bases turn red litmus  to blue
A base with a pH of 14 is
stronger than a base with
a pH of 8