Representing Representing Elements and AtomsElements and Atoms

What’s in an atom?What’s in an atom?

We now know the atom is made of 3 We now know the atom is made of 3 subatomic particlessubatomic particles

Protons (in the nucleus)Protons (in the nucleus) Neutrons (in the nucleus)Neutrons (in the nucleus) Electrons (orbits the nucleus)Electrons (orbits the nucleus)

We also know electrons orbit the nucleus in We also know electrons orbit the nucleus in specific regions, at a fixed distance from the specific regions, at a fixed distance from the centrecentre

What’s in an atom?What’s in an atom? Each subatomic particle has its own set of Each subatomic particle has its own set of

propertiesproperties

What’s in an atom?What’s in an atom? Complete the properties chart:Complete the properties chart:

NameName Relative MassRelative Mass Electric ChargeElectric Charge LocationLocation

ProtonProton 11

NeutronNeutron 11

ElectronElectron 1/1840 1/1840 (~ 0.0005)(~ 0.0005)

In the Nucleus….In the Nucleus….

Protons and neutrons contribute Protons and neutrons contribute nearly all the mass of the atomnearly all the mass of the atom

The mass of an electron is so small it is The mass of an electron is so small it is deemed “negligible”deemed “negligible”

• What does negligible mean?What does negligible mean?

Relative SizeRelative Size

Charge Charge

Every proton carries exactly the same Every proton carries exactly the same amount of positive charge (+1)amount of positive charge (+1)

Every electron carries exactly the same Every electron carries exactly the same amount of negative charge (-1)amount of negative charge (-1)

Every electron carries a negative charge Every electron carries a negative charge exactly opposite that of a proton. exactly opposite that of a proton.

Atomic NumberAtomic Number The number of protons in an atom = atomic

number

The atomic number identifies an atom as a specific element Eg. 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 NumberMass 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 ParticlesNumber of Subatomic Particles

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 ElementsShorthand Notation for Elements 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 ElementsShorthand Notation for Elements The symbol is always a capital letter first

Ar Ne B

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

the # neutrons)

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 protons Both isotopes are carbon because they each have 6 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.

How many protons, neutrons and electrons?How many protons, neutrons and electrons? ProtonsProtons- Carbon’s atomic number is 6, - Carbon’s atomic number is 6,

Therefore there are 6 protonsTherefore there are 6 protons

ElectronsElectrons- If the atom is neutral, the number of protons = - If the atom is neutral, the number of protons = the number of electronsthe number of electrons Therefore there are also 6 electronsTherefore there are also 6 electrons

NeutronsNeutrons- The mass number equals the number of protons - The mass number equals the number of protons + neutrons, + neutrons, Therefore 14-6 leaves 8 neutronsTherefore 14-6 leaves 8 neutrons

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 … …