Writing Elemental Writing Elemental SymbolsSymbolsDistinguishing Among AtomsDistinguishing Among Atoms

IntroductionIntroductionWe all know that individual We all know that individual elementselements are are different from all other different from all other elementselements..

Oxygen is different from carbon.Oxygen is different from carbon.Carbon is different from gold.Carbon is different from gold.

John Dalton’s John Dalton’s AtomicAtomic TheoryTheory stated that: stated that:““Atoms of the same element are identical and Atoms of the same element are identical and the atoms of any one element are different from the atoms of any one element are different from the atoms of any other element.”the atoms of any other element.”

Atomic NumberAtomic NumberWe now know that elements are different from We now know that elements are different from each other because they contain different each other because they contain different numbers of numbers of protonsprotons..The number of protons, pThe number of protons, p++, in the nucleus of an , in the nucleus of an atom is called the atom is called the atomicatomic number. number.Each element has its own atomic number:Each element has its own atomic number:

hydrogen has an atomic number of hydrogen has an atomic number of 11helium has an atomic number of helium has an atomic number of 22lithium has an atomic number of lithium has an atomic number of 33uranium has an atomic number of uranium has an atomic number of 9292

Mass NumberMass NumberIn addition to the atomic number, each atom of an In addition to the atomic number, each atom of an element has a element has a massmass numbernumber..

Most of the mass of an atom is in the Most of the mass of an atom is in the nucleusnucleus..The nucleus is composed of protons and The nucleus is composed of protons and neutronsneutrons, n, n00..The mass number of an atom is the The mass number of an atom is the sumsum of the of the protons and the neutrons in the nucleus.protons and the neutrons in the nucleus.

hydrogenhydrogen usually has 1 p usually has 1 p++ and 0 n and 0 n00::➠ ➠ mass number = mass number = 11

carboncarbon usually has 6 p usually has 6 p++ and 6 n and 6 n00::➠ ➠ mass number = mass number = 1212

Element SymbolsElement SymbolsThe The symbolssymbols are a shorthand way of telling us are a shorthand way of telling us what element we are dealing with.what element we are dealing with.Most symbols are based on the Most symbols are based on the commoncommon namename of of the element:the element:

HH for hydrogen for hydrogenHeHe for helium for heliumOO for oxygen for oxygenCC for carbon for carbonNN for nitrogen for nitrogen

Element SymbolsElement SymbolsSome of the symbols are based on historical, Some of the symbols are based on historical, usually latin, names:usually latin, names:

PbPb for lead (from for lead (from plumbumplumbum))FeFe for iron (from for iron (from ferrumferrum))AuAu for gold (from for gold (from aurumaurum))NaNa for sodium (from for sodium (from natriumnatrium))KK for potassium (from for potassium (from kaliumkalium))WW for tungsten (from for tungsten (from wolframwolfram [german]) [german])

Element SymbolsElement SymbolsWhen we are using the symbols to talk about an When we are using the symbols to talk about an element in a element in a chemicalchemical reactionreaction, we most often , we most often use the symbol by itself.use the symbol by itself.Sometimes, we want to know the Sometimes, we want to know the atomicatomic number number and the and the massmass number of the element we are number of the element we are working with.working with.In that case, we use the symbol with the atomic In that case, we use the symbol with the atomic number and the mass number.number and the mass number.

Element SymbolsElement SymbolsFirst, we write the First, we write the symbolsymbol..

CC

Next, we write the Next, we write the atomicatomic number in the lower left. number in the lower left.

66

Next, we write the Next, we write the massmass number in the upper left. number in the upper left.

1212

This is the complete element symbolThis is the complete element symbol

IsotopesIsotopesJohn Dalton felt that all atoms of a particular John Dalton felt that all atoms of a particular element were “element were “identicalidentical.”.”

He was wrong.He was wrong.Individual atoms of an element all have the same Individual atoms of an element all have the same atomicatomic number, the same number of number, the same number of protonsprotons..Individual atoms of an element sometimes have Individual atoms of an element sometimes have different different massmass numbers. numbers.

These are called These are called isotopesisotopes..Isotopes of an element have the same number of Isotopes of an element have the same number of protons but a different number of protons but a different number of neutronsneutrons..

IsotopesIsotopesFor example, most carbon atoms have For example, most carbon atoms have 66 protons protons and and 66 neutrons; ➠ mass number = neutrons; ➠ mass number = 1212..

CC661212

IsotopesIsotopesFor example, most carbon atoms have 6 protons For example, most carbon atoms have 6 protons and 6 neutrons; ➠ mass number = 12.and 6 neutrons; ➠ mass number = 12.

CC661212

However, some carbon atoms have However, some carbon atoms have 66 protons and protons and 77 neutrons; ➠ mass number = neutrons; ➠ mass number = 1313..

CC661313

IsotopesIsotopesFor example, most carbon atoms have 6 protons For example, most carbon atoms have 6 protons and 6 neutrons; ➠ mass number = 12.and 6 neutrons; ➠ mass number = 12.

CC661212

However, some carbon atoms have 6 protons and However, some carbon atoms have 6 protons and 77 neutrons; ➠ mass number = neutrons; ➠ mass number = 13.13.

CC661313

And, other carbon atoms have And, other carbon atoms have 66 protons and protons and 88 neutrons; ➠ mass number = neutrons; ➠ mass number = 1414..

CC661414

CountingCountingWhen we use the elemental symbols, we can When we use the elemental symbols, we can count the number of count the number of protonsprotons, , neutronsneutrons, and , and electronselectrons in an atom. in an atom.

The number of The number of protonsprotons is the same as the is the same as the atomic numberatomic number..The number of The number of neutronsneutrons is the same as the is the same as the mass numbermass number minus the atomic number. minus the atomic number.The number of The number of electronselectrons is the same as the is the same as the number of protonsnumber of protons in a neutral atom. in a neutral atom.

Ions have a different number of electrons than Ions have a different number of electrons than protons and we will cover those later.protons and we will cover those later.

CountingCountingSo, the number of So, the number of pp++ is the atomic number. is the atomic number.

CC

The mass number is the number of The mass number is the number of pp++ plus the plus the number of number of nn00..

66

The number of The number of ee-- is the same as the number of is the same as the number of pp++..

1212

# of p# of p++

# of p# of p++ plus # plus # of nof n00

# of e# of e--

CountingCountingLet’s do an example.Let’s do an example.

PP

Find the number of pFind the number of p++, n, n00, and e, and e-- in phosphorus-31. in phosphorus-31.

1515

The number of pThe number of p++ is the same as the atomic is the same as the atomic number.number.

3131 # p# p++ = = 1515

The number of eThe number of e-- is the same as the atomic is the same as the atomic number.number.

# e# e-- = = 1515

The number of nThe number of n00 is the mass number minus the is the mass number minus the atomic number.atomic number.

# n# n00 = 31 - 15 = = 31 - 15 = 1616

CountingCountingLet’s do another example.Let’s do another example.

PtPt

Find the number of pFind the number of p++, n, n00, and e, and e-- in platinum-195. in platinum-195.

7878

The number of pThe number of p++ is the same as the atomic is the same as the atomic number.number.

195195 # p# p++ = = 7878

The number of eThe number of e-- is the same as the atomic is the same as the atomic number.number.

# e# e-- = = 7878

The number of nThe number of n00 is the mass number minus the is the mass number minus the atomic number.atomic number.

# n# n00 = 195 - 78 = = 195 - 78 = 117117

CountingCountingLet’s do another example.Let’s do another example.

UU

Find the number of pFind the number of p++, n, n00, and e, and e-- in uranium-238. in uranium-238.

9292

The number of pThe number of p++ is the same as the atomic is the same as the atomic number.number.

238238 # p# p++ = = 9292

The number of eThe number of e-- is the same as the atomic is the same as the atomic number.number.

# e# e-- = = 9292

The number of nThe number of n00 is the mass number minus the is the mass number minus the atomic number.atomic number.

# n# n00 = 238 - 92 = = 238 - 92 = 146146

CountingCountingLet’s do another example.Let’s do another example.

KK

Find the number of pFind the number of p++, n, n00, and e, and e-- in potassium-40. in potassium-40.

1919

The number of pThe number of p++ is the same as the atomic is the same as the atomic number.number.

4040 # p# p++ = = 1919

The number of eThe number of e-- is the same as the atomic is the same as the atomic number.number.

# e# e-- = = 1919

The number of nThe number of n00 is the mass number minus the is the mass number minus the atomic number.atomic number.

# n# n00 = 40 - 19 = = 40 - 19 = 2121