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```Atoms - the fundamental building blocks of all stuff
neutrons – weigh about 1 au; uncharged (neutral);
found in the nucleus
protons -
weigh about 1 au; positive charge;
found in the nucleus; determine what element
the atom is
electrons – weigh about 0 (1/1840 the mass of protons);
negatively charged; found in orbitals around
the nucleus; determine what an atom does
Electrons exist in orbitals or energy levels–
distinct probability clouds around the nucleus
2 electrons fit in the first energy level
8 in each subsequent level
He
2 neutrons
2 protons
2 electrons
Cl
C
6 neutrons
6 protons
6 electrons
2 in first level, 4 in second
18 neutrons
17 protons
17 electrons
2,8, and 7 in each level
In their natural state, atoms have the same number of
protons (+) as electrons (-). Thus, they are neutral
Most atoms of a given element, have the same number
of neutrons as protons and electrons, but not always
Atoms of a given element with differing numbers of
neutrons are called isotopes
Some isotopes are stable, others tend to decay by losing
neutrons. We call this decay radioactivity.
Unstable isotopes break down at predictable rates
according to half-life
Example:
Carbon 14 has a half life of 5700 years
after 5700 years, half of the C14 in the original sample will decay
after 11400 years, ¼ of the original sample will be C14
after 17100 years, 1/8 ( ½ x ½ x ½)
after 22800 years, 1/16
etc.
Protons determine what element you have –
thus all hydrogen has 1 proton, all carbon has 6, all oxygen has 8
Electrons determine the properties of atoms and reactions with others
Neutrons are neutral –so all isotopes of a given element have the:
Same number of protons – making them the same element
The same number of electrons – making them react the same
and have the same properties
Different number of neutrons – changing nothing but the weight
Atomic mass = protons + neutrons
Atomic number = place on periodic table = number of protons
Valence electrons = number of electrons in outer level
Elements of life:
About 98% of living things is 4 elements: CHON
Composition of the Lithosphere
Oxygen
Silicon
Aluminum
Iron
Calcium
Sodium
Potassium
Magnesium
Titanium
Hydrogen
Carbon
All others
47
28
7.9
4.5
3.5
2.5
2.5
2.2
0.46
0.22
0.19
<0.1
Composition of the Human
Body
Hydrogen
63
Oxygen
25.5
Carbon
9.5
Nitrogen
1.4
Calcium
0.31
Phosphorus
0.22
Chlorine
0.03
Potassium
0.06
Sulfur
0.05
Sodium
0.03
Magnesium
0.01
All others
<0.01
Compounds
When 2 or more elements bond together in set proportions they
make compounds
Naming compounds (molecular formulae):
H20 = 2 parts hydrogen to 1 part oxygen
H2SO4 = 2 Hydrogen, 1 sulfur, 4 Oxygen (sulfuric acid)
Compounds have much different properties from their elements
Sodium is a silverish metal
Chlorine is a greenish gas
Sodium Chloride (NaCl) is table salt
Ionic bonds: electron is transferred from 1 atom to another –
this creates positively and negatively charged ions
Covalent bonds – electrons are shared among atoms
```
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