Atoms, Elements, and Molecules Image from: ase.tufts.edu
Atoms, Elements, and Molecules
Image from: ase.tufts.edu
Matter
Matter is anything that has mass and takes up space
Most of what we see is matter
Matter is made of atoms
What are atoms?
Atoms
Atoms are the smallest building blocks of matter that can chemically change This means that they are the smallest
piece of matter that has chemical properties
Since atoms make up matter, and matter makes up almost everything we know, it means almost everything is made of atoms
Atoms are made of different parts
Parts of the Atom
The atom is made of basic 3 parts:
Protons
Neutrons
Electrons
Both found in the nucleus
‘Orbits’ outside the nucleus
Parts of the Atom - Nucleus The center of the atom is called the nucleus
It holds all of the mass of the atom
There are 2 parts of the nucleus:
Protons – positively charged
Neutrons – not charged
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Parts of the Atom - Electrons Electrons ‘orbit’ outside of the
nucleus
Electrons are negatively charged
Electrons weigh about 2000 times less than protons or neutrons, so we assume the nucleus has all of the mass
Electrons orbit REALLY far away from the nucleus 6
Electrons
Electrons are really far away from the nucleus
If the nucleus were the size of a marble and that marble was placed on the middle of a soccer field, the electrons would far outside the outside of the stadium.
This means that atoms are almost entirely empty space
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Atoms and Elements There are different types of atoms
Each type of atom is called an element
There are 92 naturally occurring elements and 26 man-made elements
Each element has it’s own unique physical and chemical properties
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Elements Elements are listed on the Periodic Table of
Elements
Each elements has its own square on the Periodic Table
Each element has a 1 or 2 letter symbol called a chemical symbol The first letter is ALWAYS a capital letter The second letter (if present) is ALWAYS
lower case. 9
Chemical Symbol Examples
What are the symbols for the following elements?1. Hydrogen
2. Boron
3. Oxygen
4. Magnesium
5. Einsteinium
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What elements have the following symbols?1. C
2. Ne
3. Kr
4. Mn
5. Au
6. U
Elements and Protons The number of protons
tells us the type of element the atom is The number of
protons gives an atom its identity
Protons are abbreviated p+
The number of protons in the nucleus of atom is the Atomic Number
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OOxygen
8
16.00
Atomic Number = Number of Protons
The atomic number MUST be a positive integer
Element Examples
How many protons do the following elements have?
1. Oxygen
2. Fluorine
3. Titanium
4. Sodium
5. Silver
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Which elements have the following atomic numbers?
1. 24
2. 58
3. 11
4. 100
5. 3
Elements and Neutrons Neutrons are uncharged particles in the
nucleus Neutrons are abbreviated n0
When you add the number of protons with the number of neutrons, you get the Atomic Mass
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OOxygen
8
16Atomic Mass
Atomic Mass
(# of p+) + (# of n0) = Atomic Mass Eg. Oxygen (# of p+) + (# of n0) = Atomic Mass (8) + (# of n0) = 16 (# of n0) = 8 Oxygen-16 has 8 neutrons in its nucleus
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OOxygen
8
16 Atomic Mass
Atomic Number = Number of Protons
Atomic Mass Examples
What is the atomic mass of the following atoms?1. Nitrogen with 8 n0
2. Calcium with 20 n0
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Elements always have the same number of protons but can have different numbers of neutrons in their nucleus
The same element, with different numbers of neutrons are called Isotopes
Eg. All carbon atoms have 6 protons, but they can have 6, 7, or 8 neutrons. Carbon-12, Carbon-13, and Carbon-14 are all isotopes of carbon 16
Neutrons
Atomic Mass Example
Eg. How many neutrons are in the following isotopes of Calcium?
Calcium-40
Calcium-42
Calcium-48
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Atomic Mass as an Integer
Since the atomic mass is the sum of 2 integers (number of protons and number of neutrons), the atomic mass is ALWAYS an integer
It is an irrational number on your periodic table it is because that is an average of the masses of isotopes
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Electrons Electrons determine the behaviour of an
element They give an element its physical and
chemical properties
The number of electrons is usually the same as the number of protons
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Electron Examples
How many electrons would the following atoms have?1. Nitrogen
2. Helium
3. Potassium
4. Molybdenum
5. Bohrium
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What elements have the number of electrons?1. 6
2. 11
3. 42
4. 56
5. 96
Electrons
Remember when I said that atoms have the same number of electrons and protons…
That’s not always the case
Electrons
Atoms can change their number of electrons frequently
This is because electrons are held loosely by the nucleus
This is also really important because if they couldn’t, we wouldn’t be alive!
Electrons
Atoms are called neutral if they have the same number of protons and electrons
This is because if an atom have the same number of protons and electrons, the atom has no charge
Eg. – Hydrogen Has 1 proton and 1 electron
(+1) + (-1) = 0
No charge is neutral
Ions
Atoms that lose or gain electrons are called ions
Ions have a charge
When writing the charge, it always goes in the top right-hand corner. Eg. Fluorine with a -1 charge gets is shown as:
F-
Eg. Selenium with a charge of -2 is shown as:
Se2-
Cations
If an atom loses electrons, it gets a positive charge
Atoms with a positive charge are called cations
Cation Examples
1) How many electrons would each of the following have? Beryllium loses 2 electrons Sodium loses 1 electron
2) What is the charge on each of the following atoms? Aluminum loses 3 electrons Silicon loses 4 electrons
Anions
If an atoms gains electrons, it gets a negative charge
Atoms with a negative charge are called anions Think of it like this, A-Negative-ion, A-N-ion
Anion Examples
1) How many electrons would each of the following have?– Fluorine gains 1 electron– Phosphorus gains 3 electrons
2) What is the charge on each of the following atoms?– Sulphur gains 2 electrons– Chlorine gains 2 electrons
Can we go smaller?
If matter is made of atoms; and atoms are made of protons, neutrons, and electrons; what are protons, neutrons, and electrons made of?
How small can we go?
Compounds So far we learned about elements, 1 type of pure
substance
The other type of pure substance is a compound
Compounds are 2 or more elements hooked (sometimes called bonded) together
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Compounds Compounds are made of 2 or more
combined elements
However, they have completely different chemical and physical properties than the elements they are made of
Example – Sodium is a silver metal that explodes when it touches water. Chlorine is a poisonous gas that destroys lung tissue. Sodium Chloride is salt and is necessary for life
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Chemical Formulas
Molecules are another name for compounds
All compounds are represented with a special notation Write the chemical symbol of each element in
the compound If there is only 1 atom of that element in the
compound, leave it alone If there are 2 or more atoms of an element,
write a small number in the bottom right hand of the chemical symbol 32
Writing Chemical Formulas Example – Write the chemical formula for Calcium
Carbonate. It is 1 calcium, 1 carbon, and 3 oxygens.
Write the chemical symbol of each element Ca C O
Write the number of the atoms in the bottom right corner of the chemical symbol
CaCO3
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Chemical Formula Examples Write the chemical
formula for each compound1. Hydroiodic acid – 1
hydrogen, 1 iodine
2. Hydrogen Peroxide – 2 hydrogen, 2 oxygens
3. Glucose – 6 carbon, 12 hydrogen, 6 oxygen
4. Sulphuric Acid – 2 hydrogen, 1 sulphur, 4 oxygen
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Determine which elements, and how many of each, are in the following compounds1. BaCl2
2. N2
3. Fe2O3
4. KCo2F5
5. U3O8