Representing Elements and Atoms

Atomic Number

The number of protons in an atom = atomic number

The atomic number identifies an atom as a specific element Ex. Atomic number = 6 means this atom has 6

protons in it Only carbon has 6 protons If a proton is somehow added to this atom, it

is no longer carbon. It becomes nitrogen (atomic number 7), a completely different element

Mass Number

Mass number = # protons + # neutronsMass number = # protons + # neutrons

If I know the mass number, how can I determine the number of neutrons in an atom? # neutrons = mass number – atomic number

= total # P & N – # P # neutrons in Na = 23 – 11

= 12

Number of Subatomic Number of Subatomic ParticlesParticles

So far, you have learned how to find the number of protons and neutrons in an atom.

Now, how do you find the number of electrons? In a neutral atom, positive charge =

negative charge Therefore, # protons must = # electrons

since they have equal but opposite charge

Number of ElectronsNumber of Electrons

Ex. In a neutral carbon atom, how many electrons are there? Carbon’s atomic number is 6.

Therefore, there are 6 protons. Since there are 6 protons, there must

also be 6 electrons to balance the charge• (+6) + (-6) = 0

6 protons x (+1) charge each

6 electrons x (-1) charge each

Gives you an atom with no overall charge

Shorthand Notation for Shorthand Notation for ElementsElements

The same way it is easier to write 5678 instead of five thousand six hundred seventy-eight, we need a shortcut for atoms of elements

Each element has its own symbol. This is a universal ‘language’ for all scientists. Na sodium K potassium C carbon

Shorthand Notation for Shorthand Notation for ElementsElements

The symbol is always a capital letter first Ar Ne B

In “Standard Atomic Notation”: Mass number goes at the top Atomic number goes below

IsotopesIsotopes Isotopes: AIsotopes: Atoms with the same number of protons toms with the same number of protons

but a different number of neutrons.but a different number of neutrons. Different varieties of the same elementDifferent varieties of the same element

2 common isotopes are Carbon-14 and Carbon-12.2 common isotopes are Carbon-14 and Carbon-12. Both isotopes are carbon because they each have 6 Both isotopes are carbon because they each have 6

protons protons 

They are different because C-14 has 8 neutrons and They are different because C-14 has 8 neutrons and C-12 only has 6C-12 only has 6

While C-12 is the most abundant (common) isotope While C-12 is the most abundant (common) isotope of carbon, both are called isotopesof carbon, both are called isotopes

IsotopesIsotopes Here is the isotopic notation for carbon 14.Here is the isotopic notation for carbon 14.

From looking at the isotopic notation, you can determine From looking at the isotopic notation, you can determine the number of protons, neutrons and electrons for a given the number of protons, neutrons and electrons for a given atom.atom.

How many protons, neutrons and electrons?How many protons, neutrons and electrons? ProtonsProtons- The atomic number is 6, therefore there are 6 - The atomic number is 6, therefore there are 6

protonsprotons ElectronsElectrons- If the atom is neutral, the number of protons - If the atom is neutral, the number of protons

= the number of electrons, therefore there are also 6 = the number of electrons, therefore there are also 6 electrons.electrons.

NeutronsNeutrons- The mass number equals the number of - The mass number equals the number of protons + neutrons, therefore 14-6 leaves 8 neutronsprotons + neutrons, therefore 14-6 leaves 8 neutrons . .

Shorthand Notation for Shorthand Notation for ElementsElements

Your text book tries to simplify… They have AM on the bottom and AN on the top

Remember: Atomic number = a whole number (no decimal) Atomic mass = usually a decimal (an average of the #

neutrons)

Write the standard atomic notation for Hydrogen Calcium Oxygen

(Hint: Use your periodic table!)

Standard Atomic NotationStandard Atomic Notation

Homework: Learn the first 20 symbols Learn the first 20 element names in order

(Atomic numbers 1-20) Spelling included!

HomeworkHomework

Element symbol Element name

1 H Hydrogen

2 He Helium

3 Li Lithium

4 … …

5 … …

…etc … …