Transcript Atoms and Elements - Effingham County Schools

What’s the MATTER?
Anything that has mass and takes up space
What about air ….
Slice and
dice it to as
small a
piece you
can make
it……..
atom
An atom has a
positively charged
center surrounded by
a negatively charged
area.
Electron
cloud
6e–
++
Nucleus
6 + Protons
+
-
6
Neutrons
6 – Electrons
Mass
number = 12
3 subatomic particles….. 2 regions
1. nucleus (positiive region)
protons (positive) and neutrons (neutral)
2. electron clouds (negative region)
electrons (negative)
– –
2e–
+
+
+
+
Electron
cloud
Nucleus
2 + Protons
2
Neutrons
2 – Electrons
Mass
number = 4
protons
p.p.p.p.p.pppositive
PP ….. Ewe….
neutrons
Electrons(-)
NEUTRAL
It’s electric …
no thanks..
Atoms and Elements
ELEMENTS, ATOMS, AND
MOLECULES
• Living organisms are composed of about 25
chemical elements
– About 25 different chemical elements
•
Are essential to life
– About 90 naturally occurring elements
•
Listed on the periodic table with some unnatural
ones
•
How many different naturally
occuring elements are there?
a. About 25
b. About 90
c. Over 1000
Atoms and Elements
• Horizontal rows are called periods.
• Vertical columns are called groups.
•Differences in Elements
– Atoms of each element
•
Are distinguished by a specific number of protons
IRON
Atomic number
Symbol
Atomic mass
IRON
Atomic Mass ------ 56
Atomic number ------- 26
Protons -------- 26
Neutrons -------- 30
Electrons -------- 26
– Carbon, hydrogen, oxygen, and nitrogen
•
Make up the bulk of living matter
•Trace elements are common additives to
food and water
– Dietary deficiencies in trace elements
•
Can cause various physiological conditions
– Trace elements are essential to human
health
•
And may be added to food or water
•
Which elements are the most
common in living things?
a. Carbon, Helium, Chlorine and Sulfur
b. Hydrogen, Carbon, Nitrogen and Calcium
c. Carbon, Oxygen, Nitrogen and Hydrogen
•
What’s makes gold gold and lead
lead?
a. The number of protons
b. The number of neutrons
c. The number of electron
•Isotopes
– The number of neutrons in an atom may vary
•
Variant forms of an element are called isotopes
•
Some isotopes are radioactive
Table 2.4
•Electron arrangement determines
the chemical properties of an atom
Outermost electron shell (can hold 8 electrons)
First electron shell (can hold 2 electrons)
Electron
Hydrogen (H)
Atomic number = 1
Carbon (C)
Atomic number = 6
Nitrogen (N)
Atomic number = 7
Oxygen (O)
Atomic number = 8
– Atoms whose shells are not full
•
Tend to interact with other atoms and
gain, lose, or share electrons
– These interactions
•
Form chemical bonds
•
Why do atoms form bonds to make
molecules?
a. To gather more protons for their nuclei
b. To increase the number of their electrons
c. To have a stable number of electrons in their
outermost shell
Elements can combine to form compounds
– Chemical elements
•
•
Combine in fixed ratios to form compounds
Millions of different molecules possible
Sodium
Chlorine
Sodium Chloride
MATTER
element
compound
Pure substance can be
found in nature
Pure substance formed
when two or more different
elements combine.
atom
molecule
molecules
_
O
H
+
H
+
•Ionic bonds are attractions between ions
of opposite charge
– When atoms gain or lose electrons
•
–
Charged atoms called ions are created
–
+
Transfer of
electron
–
Na
Cl
Na
Sodium atom
Cl
Chlorine atom
Na
Cl
Na+
Sodium ion
Cl–
Chloride ion
Sodium chloride (NaCl)
– An electrical attraction between ions with
opposite charges
•
–
Results in an ionic bond
–
+
Transfer of
electron
Na
Cl
Na
Sodium atom
Cl
Chlorine atom
–
Na
Cl
Na+
Sodium ion
Cl–
Chloride ion
Sodium chloride (NaCl)
– Sodium and chloride ions
•
Bond to form sodium chloride, common table salt
Na+
Cl–
• Ionic Bonding
•Covalent bonds join atoms into
molecules through electron sharing
covalent bonds
Oxygen atom (O)
Carbon atom (C)
Carbon dioxide (CO2 )
Oxygen atom (O)
Molecules can
be represented
in many ways
•Unequal electron sharing creates polar
molecules
– A molecule is nonpolar
•
(–)
When its covalently bonded atoms share
electrons equally
(–)
O
H
(+)
H
(+)
– In a polar covalent bond
•
Electrons are shared unequally between atoms,
creating a polar molecule
(–)
(–)
O
H
H
(+)
(+)
Figure 2.9
• Hydrogen bonds are weak bonds
important in the chemistry of life
– The charged regions on water molecules
•
Are attracted to the oppositely charged
regions on nearby molecules
(–)
(–)
O
H
(+)
H
(+)
– This attraction forms weak bonds
•
Called hydrogen bonds
(–)
Hydrogen bond
(+)
H
(+)
O
(–)
H
(–)
(+)
(–)
(+)
•
1. What type of bond is formed by
sharing electrons?
a. Hydrogen
b. Covalent
c. Ionic
•
2. What type of bond is very weak
but important to holding together
DNA?
a. Hydrogen
b. Covalent
c. Ionic
•
3. What type of strong bond does
salt make from sodium and
chlorine?
a. Hydrogen
b. Covalent
c. Ionic
4. Why do atoms of elements form chemical
bonds with other atoms to form
molecules?
a. To fill their nucleus with a stable number of
protons
b. To fill the outer shell of their atoms with a
stable number of electrons
c. To add to the number of neutrons in their
nucleus
5. Water is a molecule formed from
Oxygen and 2 Hydrogen sharing
electrons. What type of bond is
this?
a. Covalent
b. Hydrogen
c. Ionic
6. What makes each element unique is
the number of protons it has in its
nucleus.
True or False
7. Which type of chemical bonding is
weakest?
a. Covalent
b. Ionic
c. Hydrogen