Isotopes and Ions. Quotes about atoms From A Short History of Nearly Everything by Bill Bryson...
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Transcript of Isotopes and Ions. Quotes about atoms From A Short History of Nearly Everything by Bill Bryson...
Isotopes and Ions
Quotes about atomsQuotes about atomsFrom From A Short History of Nearly A Short History of Nearly Everything Everything by Bill Bryson by Bill Bryson
““protons give an atom its protons give an atom its identity, electrons its identity, electrons its personality” p. 140personality” p. 140““if an atom were expanded if an atom were expanded to the size of a cathedral, to the size of a cathedral, the nucleus would be only the nucleus would be only about the size of a fly- but about the size of a fly- but a fly many thousands of a fly many thousands of times heavier than the times heavier than the cathedral” p. 141cathedral” p. 141
Parts of the atom:Proton:– + charge– Located in nucleus– Role: identifies the atom
Neutron:– no charge– Located in nucleus– Role: space out nucleus and add mass (stabilize the
nucleus)
Electron:– - charge– Located in orbital's outside of nucleus (energy levels)– Role: perform all bonding of atom, give it charge
Atom Model
Atomic Number
Found at top of each element square
Represents the number of protons in atom
If atom is “neutral” number of protons = number of electrons
Atomic Mass# at bottom of each element box
= # of protons + # of neutrons
To find # neutrons, subtract atomic number from atomic mass
Ex) C: atomic mass = 12, atomic # = 6,– # of protons = 6,– # of neutrons = 6, (12-6)– # of electrons = 6 (= to # of protons)
Atomic Symbols
Shorthand way of writing information
Write symbol for element
Put atomic number in subscript in front of symbol
Put atomic mass in superscript in front of symbol
BASICALLY FLIPPED FROM P.T.
Atomic Symbol Example
What is an ion?Ion - an atom or group of atoms that has a positive or negative charge
An ion forms when an atom gains or loses electrons (protons identify atom)
How does an atom become an ion?
What is the charge on an electron?– negative
If you have more electrons than protons the charge would be?– negative
If you have more protons than electrons?– positive (extra protons)
CationPositive charge– Cat-ions are pawwwwwsitive
Formed by the atom losing electrons
Metals (left side of periodic table) form cations
Ca Ca2+ + 2e-
How many electrons did Ca start with?
How many did it end with?20
18
Anion
Negative charge– An-ion is a negative ion
Formed by the atom gaining electrons
Non-metals (right side of periodic table) form anions
O + 2e- O2-
How many electrons did O start with?
How many did it end with?
810
Key Point
If atom has more p+ than e-, it will be a cation, have a + charge
If atom has more e- than p+, it will be anion, have a - charge
Ion atomic Symbol
Can always tell p+, no, e- from atomic symbol,
Must include charge for ion!– Atomic # & atomic mass go on the LEFT– Charge goes on the RIGHT
Ex: Al+3
– How many protons, electrons and neutrons?
€
13
27
What is an isotope?
Isotopes are atoms of the same element with different atomic masses.
They have different masses because they have different numbers of neutrons in the nucleus (remember, neutrons add mass and stability to the atom)
How do you write isotopes?There are different types of isotope notation:
Carbon-14 C C
These all tell us that we are dealing with an isotope of carbon with an atomic mass of 14.
How many protons and neutrons are in these isotopes? – Protons = 6– Neutrons = 14 – 6 =8
€
14
€
614
How many protons and neutrons in these?
O
N
Hydrogen-3
€
816
€
15
protons = 8, neutrons = 16 – 8 = 8
protons = 7, neutrons = 15 - 7 = 8
protons = 1, neutrons = 3 -1 = 2
Ions & Isotopes
Both ions and isotopes can be shown in the same symbol.– Atomic # & atomic mass go on the LEFT– Charge goes on the RIGHT
– How many protons, neutrons and electrons
S
€
34
€
−2 Protons= 16Neutrons = 34-16 = 18Electrons = 16 +2 = 18
Write your own
Write symbols for the following:
The ion with 17 protons, 18 electrons, 20 neutrons:
The ion with 92 protons, 88 electrons, 146 neutrons:
Cl-
€
1737
€
−
U+4
€
92238
Key Points (atomic symbols)
Mass Number (# on top) – use to find neutrons
Atomic Number (# on bottom) – use to find protons
Charge Symbol (to right) – use to find electrons
Average atomic mass
So far all the atomic masses we have used have been whole numbers
BUT there are not whole number masses on the periodic table
WHY??? The numbers on the periodic table are AVERAGE atomic masses
Calculating average atomic mass
Average atomic mass is calculated by taking the average of all the different isotope masses
For example, if these were the only 5 atoms of carbon we had:Carbon-12, Carbon-12, Carbon-12, Carbon-14, Carbon-14
What would the average mass be?
– 12+12+12+14+14 / 5 = 12.8
We can’t possibly weigh every atom in the world though…So we have to average their abundances– How much of them exists in relation to total
Using our example from before:Carbon-12, Carbon-12, Carbon-12, Carbon-14, Carbon-14
Abundance of carbon-12 = 3/5 = (0.60 relative abundance) 60%
Abundance of carbon-14 = 2/5 = (0.40 relative abundance) 40%
Calculate average mass: 12g(0.60) + 14g(0.40) = 12.8g
SAME ANSWER!!! LESS WORK!!
Practice Problem #1Calculate the average atomic mass of magnesium using the following data for three magnesium isotopes.
Isotope mass (amu) % abundance
Mg-24 23.985 78.70
Mg-25 24.986 10.13
Mg-26 25.983 11.17
Practice Problem #2
Calculate the average atomic mass of lithium, which occurs as two isotopes that have the following atomic masses and abundances in nature:
Lithium-6, 6.017 amu, 7.30%
Lithium-7, 7.018 amu, 92.70%
Key Points
% of all isotopes has to add up to 100!
Make sure to take %’s and convert to relative abundance (move decimal 2 places to right)
What happens when you change…What happens when you change…Protons: Protons: number of protons is the same as the number of protons is the same as the atomic number, protons are what define an atomic number, protons are what define an element.element.– change the protons you change the elementchange the protons you change the elementNeutrons: Neutrons: The neutrons add to the mass and The neutrons add to the mass and stability to the element.stability to the element.– change the mass of the element (make an change the mass of the element (make an
isotope)isotope)Electrons: Electrons: The electrons balance the charge of The electrons balance the charge of the protons.the protons.– change the charge of the element (make an change the charge of the element (make an
ion)ion)
Marshmallium Lab
On the BACK:– Calculate average marshmallow mass
using the LONG way• Find the mass of each marshmallow, add them
all up and divide by the total number of marshmallows
– Write a sentence about why the way on the front (read directions) is easier.