Post on 11-May-2015
transcript
Inside The
Atom
Structure of the Atom
• There are two regions• The nucleus• With protons and neutrons • Positive charge• Almost all the mass• Electron cloud- Most of the volume of an
atom• The region where the electron can be
found
Subatomic particles
Electron
Proton
Neutron
Name Symbol Charge
Relative mass
Actual mass (g)
e-
p+
n0
-1
+1
0
1/1840
1
1
9.11 x 10-28
1.67 x 10-24
1.67 x 10-24
Size of an atom• Atoms are small.• Measured in picometers, 10-12 meters• Hydrogen atom, 32 pm radius• Nucleus tiny compared to atom• IF the atom was the size of a stadium,
the nucleus would be the size of a marble.
• Radius of the nucleus near 10-15m.• Density near 1014 g/cm
Counting the Pieces
• Atomic Number = number of protons
• # of protons determines kind of atom
• the same as the number of electrons in the neutral atom
• Mass Number = the number of protons + neutrons
• All the things with mass
Symbols• Contain the symbol of the element, the
mass number and the atomic number
• THIS IS NOT THE SAME AS WHAT IS IN THE PERIODIC TABLE!
X Massnumber
Atomicnumber
Symbols
• Find the – number of protons– number of neutrons– number of electrons– Atomic number– Mass Number
F19 9
SymbolsSymbols Find the Find the
–number of protonsnumber of protons
–number of neutronsnumber of neutrons
–number of electronsnumber of electrons
–Atomic numberAtomic number
–Mass NumberMass Number
Br80 35
SymbolsSymbols if an element has an atomic if an element has an atomic
number of 34 and a mass number of 34 and a mass number of 78 what is the number of 78 what is the
–number of protonsnumber of protons
–number of neutronsnumber of neutrons
–number of electronsnumber of electrons
–Complete symbolComplete symbol
SymbolsSymbols if an element has 91 protons if an element has 91 protons
and 140 neutrons what is the and 140 neutrons what is the
–Atomic numberAtomic number
–Mass numberMass number
–number of electronsnumber of electrons
–Complete symbolComplete symbol
Ions
• Under normal conditions, atoms have the same number of electrons as protons
• When atoms react chemically, they can gain or loose electrons
• When an atom has gained or lost an electronit is now considered an ion
A neutral atom of sodium has 11 protons and 11 electrons
When sodium reacts chemically, it typically looses one electron; giving it 11 protons and 10 electrons
Remember: each proton has a positive charge +
each electron has a negative charge -
Sodium ION with 11 protons (11 +) and 10 electrons (10-)Now has a NET charge of (1+)
A neutral atom of chlorine has 17 protons and 17 electrons
When chlorine reacts chemically, it typically gains one electron; giving it 17 protons and 18 electrons
Remember: each proton has a positive charge +
each electron has a negative charge -
Chlorine ION with 17 protons (17 +) and 18 electrons (18-)Now has a NET charge of (1-)
Li 3
6 A neutral atom of lithium has 3 protons and 3 electrons
When lithium reacts chemically, it typically looses one electron; giving it 3 protons and 2 electrons
Remember: each proton has a positive charge +
each electron has a negative charge -
Lithium ION with 3 protons (3 +) and 2 electrons (2-)
Now has a NET charge of (1+)
Li 3
6 1 +
Li 3
6
1 +
Li 3
6
If no charge here: ATOM NEUTRAL (same number of protons as electrons)
If charge here: IONPos charge = more protons than
electronsNeg charge = more electrons than
protons
Isotopes
• Dalton was wrong.
• Atoms of the same element can have different numbers of neutrons
• different mass numbers
• called isotopes
3 protons; 3 neutrons
Mass # 6
3 protons; 4 neutrons
Mass # 7
BOTH Li
Naming Isotopes
• Put the mass number after the name of the element
• carbon- 12
• carbon -14
• uranium-235
Atomic Mass
• How heavy is an atom of oxygen?
• There are different kinds of oxygen atoms.
• More concerned with average atomic mass.
• Based on abundance of each element in nature.
• Don’t use grams because the numbers would be too small
Measuring Atomic Mass
• Unit is the Atomic Mass Unit (amu)• One twelfth the mass of a carbon-12 atom. • Each isotope has its own atomic mass we
need the average from percent abundance.
Atomic Mass
• Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the res has a mass of 64.93 amu.
Atomic Mass
• Magnesium has three isotopes. 78.99% magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 with a mass of 24.9858 amu, and the rest magnesium 25 with a mass of 25.9826 amu. What is the atomic mass of magnesium?
• If not told otherwise, the mass of the isotope is the mass number in amu
Atomic Mass
• Is not a whole number because it is an average.
• are the decimal numbers on the periodic table.
6
C12.01
Na 11
23 + 11 protons; 10 electrons
S 16
32 2- 16 protons; 18 electrons
Al 13
27 3+ 13 protons; 10 electrons
N 714 3-
How Many Protons, Neutrons, and Electrons????
Ca 2041 2+
Cl 1733 1-