AtomsAtoms

Atomic NumberAtomic Number

Identifies the element Identifies the element Atomic # = #protons= # electronsAtomic # = #protons= # electrons Is the number of protons in the Is the number of protons in the

nucleus of each atom of the element nucleus of each atom of the element In a periodic table the atomic number In a periodic table the atomic number

is above the symbol of the elementis above the symbol of the element http://http://

education.jlab.org/qa/pen_number.hteducation.jlab.org/qa/pen_number.htmlml

Mass NumberMass Number Is the total number of protons and Is the total number of protons and

neutrons in the nucleusneutrons in the nucleus Helps to identify an Isotope (atoms of Helps to identify an Isotope (atoms of

the same elements with different the same elements with different masses)masses)

Mass # - Atomic # = # of neutrons Mass # - Atomic # = # of neutrons Which will identify isotopesWhich will identify isotopes Example: How many protons, electrons and Example: How many protons, electrons and

neutrons are there in an atom of chlorine-neutrons are there in an atom of chlorine-37? 37?

37 – 17(atomic # =protons and 37 – 17(atomic # =protons and electrons) electrons) =20 neutrons=20 neutrons

IsotopesIsotopes

IsotopesIsotopes are atoms of the same element that are atoms of the same element that have different masses.have different masses.

The isotopes of a particular element all have The isotopes of a particular element all have the same number of protons and electrons the same number of protons and electrons but different numbers of neutrons.but different numbers of neutrons.

Most of the elements consist of mixtures of Most of the elements consist of mixtures of isotopes.isotopes.

IsotopesIsotopes Worksheet to be worked on in classWorksheet to be worked on in class

Molar MassMolar Mass

The mass of one mole of a pure The mass of one mole of a pure substance is called the molar mass of substance is called the molar mass of that substance.that substance.

Molar mass is usually written in units Molar mass is usually written in units of g/mol.of g/mol.

The molar mass of an element is The molar mass of an element is numerically equal to the atomic mass numerically equal to the atomic mass of the element in atomic mass unitsof the element in atomic mass units

The MoleThe Mole

A A molemole (abbreviated mol) is the (abbreviated mol) is the amount of a substance that contains amount of a substance that contains as many particles as there are atoms as many particles as there are atoms in exactly 12 g of carbon-12.in exactly 12 g of carbon-12.

The mole is the SI unit for amount of The mole is the SI unit for amount of substancesubstance

Avogadro’s NumberAvogadro’s Number

Avogadro’s numberAvogadro’s number—6.022 1415 × 10—6.022 1415 × 102323—is —is the number of particles in exactly one mole of the number of particles in exactly one mole of a pure substance.a pure substance.

Avogadro’s number can be used to find the Avogadro’s number can be used to find the number of atoms of an element from the number of atoms of an element from the amount in moles or to find the amount of an amount in moles or to find the amount of an element in moles from the number of atoms.element in moles from the number of atoms.

In these calculations, Avogadro’s number is In these calculations, Avogadro’s number is expressed in units of atoms per mole.expressed in units of atoms per mole.

Relating Mass to Numbers of Relating Mass to Numbers of AtomsAtoms

How many moles of silver, Ag, are in How many moles of silver, Ag, are in 3.01x103.01x102323atoms of silver?atoms of silver?

Ag atoms x mol Ag/Avogadro’s # of Ag Ag atoms x mol Ag/Avogadro’s # of Ag atomsatoms

= moles of Ag= moles of Ag

3.01x103.01x102323Ag atoms x1 mol Ag atoms x1 mol Ag/6.022x10Ag/6.022x102323Ag atomAg atom

=0.500 mol Ag=0.500 mol Ag

Solving Mole ProblemsSolving Mole Problems

Gram/Mole ConversionsGram/Mole Conversions Chemists use molar mass as a conversion Chemists use molar mass as a conversion

factor in chemical calculations.factor in chemical calculations. For example, the molar mass of helium is For example, the molar mass of helium is

4.00 g He/mol He.4.00 g He/mol He. For example, how many grams of He are in For example, how many grams of He are in

2.00 mol of He?2.00 mol of He?

4.00 g He2.00 mol He = 8.00 g He

1 mol He

Page 83Page 831.1. 2.25 mol Fe x 55.85g Fe/1mol Fe= 126g Fe2.25 mol Fe x 55.85g Fe/1mol Fe= 126g Fe2.2. 0.375 mol K x 39.10g K/1 mol K= 14.7g K0.375 mol K x 39.10g K/1 mol K= 14.7g K3.3. 0.0135 mol Na x 23.0g Na/1mol 0.0135 mol Na x 23.0g Na/1mol

Na=0.310gNaNa=0.310gNa4.4. 16.3 mol Ni x 58.70gNi/1 mol Ni= 958g Ni16.3 mol Ni x 58.70gNi/1 mol Ni= 958g Ni

1.1. 5.00g Ca x 1 mol Ca/40.08g Ca= 0.125 5.00g Ca x 1 mol Ca/40.08g Ca= 0.125 molCamolCa

2.2. 3.60x103.60x10-10-10gAu x 1 mol Au/196.97g Au=gAu x 1 mol Au/196.97g Au=1.83x101.83x10-12-12mol Aumol Au

Solving MoleSolving Mole How many moles of lead (Pb) are in How many moles of lead (Pb) are in

1.50 x 101.50 x 101212 atoms of lead? atoms of lead?

1.50 x 101.50 x 101212Pb atoms x 1mol Pb/6.022 x 10Pb atoms x 1mol Pb/6.022 x 1023 23 Pb Pb atomsatoms

= 2.49 x 10= 2.49 x 10-12 -12 mol Pbmol Pb

Mol to Atom ConversionsMol to Atom Conversions

amount of substance x amount of substance x 6.022x106.022x102323atomsatoms given in mol given in mol 1 mol1 mol

= answer in atoms= answer in atoms

How many atoms of sulfur are in 4.00 g How many atoms of sulfur are in 4.00 g of S?of S?

How do we start?How do we start?

What is given?What is given?

What are we solving?What are we solving?

Atom to Mol ConversionsAtom to Mol Conversions

Amount of substance x Amount of substance x 1 mol1 mol

given in atoms 6.022 x10given in atoms 6.022 x102323 atomsatoms

= answer in mol= answer in mol

How many moles of tin,Sn, are in How many moles of tin,Sn, are in 2500 atoms of tin?2500 atoms of tin?

How do we start?How do we start?

What is given?What is given?

What are we solving?What are we solving?

Mol to Mass ConversionsMol to Mass Conversions

Amount of substance x Amount of substance x molar mass of molar mass of element(g)element(g)

given in molgiven in mol 1 mol 1 mol

= answer in grams= answer in grams

Remember molar mass unit is g/mol and is Remember molar mass unit is g/mol and is the atomic mass on the periodic tablethe atomic mass on the periodic table

What is the mass in grams of 0.0135 What is the mass in grams of 0.0135 mol of sodium?mol of sodium?

Mass to Mol ConversionsMass to Mol Conversions

Amount of substance xAmount of substance x 1mol 1mol

given in mass (g)given in mass (g) molar mass molar mass (g)(g)

=answer in mol=answer in mol

How many moles of gold are in How many moles of gold are in 3.60x103.60x10-10 -10 g of Au?g of Au?

Mass to Atom ConversionsMass to Atom Conversions

Amt of substance x Amt of substance x 1mol 1mol xx 6.022x106.022x102323atomatom

given in mass (g)given in mass (g) molar mass 1 molar mass 1 molmol

= answer in atoms= answer in atoms

How many atoms of sulfur are in How many atoms of sulfur are in 4.00g of S?4.00g of S?

Atom to Mass ConversionsAtom to Mass Conversions

Amt. of substance x Amt. of substance x 1mol 1mol x x molar molar mass(g) mass(g)

given in atoms 6.022x10given in atoms 6.022x102323atom 1 molatom 1 mol

=answer in mass (g)=answer in mass (g)

What is the mass in grams of What is the mass in grams of 1.50x101.50x102323atoms of tin?atoms of tin?