Atoms

Atomic Number Identifies the element Atomic # = #protons= # electrons Is the number of protons in the nucleus of each atom of the element In a periodic table the atomic number is above the symbol of the element http://education.jlab.org/qa/pen_number.html

Mass Number Is the total number of protons and neutrons in the nucleus Helps to identify an Isotope (atoms of the same elements with different masses) Mass # - Atomic # = # of neutrons Which will identify isotopes Example: How many protons, electrons and neutrons are there in an atom of chlorine-37? 37 – 17(atomic # =protons and electrons) =20 neutrons

Isotopes Isotopes are atoms of the same element that have different masses. The isotopes of a particular element all have the same number of protons and electrons but different numbers of neutrons. Most of the elements consist of mixtures of isotopes. Isotopes Worksheet to be worked on in class

Molar Mass The mass of one mole of a pure substance is called the molar mass of that substance. Molar mass is usually written in units of g/mol. The molar mass of an element is numerically equal to the atomic mass of the element in atomic mass units

The Mole A mole (abbreviated mol) is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12. The mole is the SI unit for amount of substance

Avogadro’s Number Avogadro’s number—6.022 1415 × 1023—is the number of particles in exactly one mole of a pure substance. Avogadro’s number can be used to find the number of atoms of an element from the amount in moles or to find the amount of an element in moles from the number of atoms. In these calculations, Avogadro’s number is expressed in units of atoms per mole.

Relating Mass to Numbers of Atoms How many moles of silver, Ag, are in 3.01x1023atoms of silver? Ag atoms x mol Ag/Avogadro’s # of Ag atoms = moles of Ag 3.01x1023Ag atoms x1 mol Ag/6.022x1023Ag atom =0.500 mol Ag

Solving Mole Problems

Gram/Mole Conversions Chemists use molar mass as a conversion factor in chemical calculations. For example, the molar mass of helium is 4.00 g He/mol He. For example, how many grams of He are in 2.00 mol of He?

Page 83 2.25 mol Fe x 55.85g Fe/1mol Fe= 126g Fe 0.375 mol K x 39.10g K/1 mol K= 14.7g K 0.0135 mol Na x 23.0g Na/1mol Na=0.310gNa 16.3 mol Ni x 58.70gNi/1 mol Ni= 958g Ni 5.00g Ca x 1 mol Ca/40.08g Ca= 0.125 molCa 3.60x10-10gAu x 1 mol Au/196.97g Au= 1.83x10-12mol Au

Solving Mole How many moles of lead (Pb) are in 1.50 x 1012 atoms of lead? 1.50 x 1012Pb atoms x 1mol Pb/6.022 x 1023 Pb atoms = 2.49 x 10-12 mol Pb

Mol to Atom Conversions amount of substance x 6.022x1023atoms given in mol 1 mol = answer in atoms

How many atoms of sulfur are in 4.00 g of S? How do we start? What is given? What are we solving?

Atom to Mol Conversions Amount of substance x 1 mol given in atoms 6.022 x1023 atoms = answer in mol

How many moles of tin,Sn, are in 2500 atoms of tin? How do we start? What is given? What are we solving?

Mol to Mass Conversions Amount of substance x molar mass of element(g) given in mol 1 mol = answer in grams Remember molar mass unit is g/mol and is the atomic mass on the periodic table

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

Mass to Mol Conversions Amount of substance x 1mol given in mass (g) molar mass (g) =answer in mol

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

Mass to Atom Conversions Amt of substance x 1mol x 6.022x1023atom given in mass (g) molar mass 1 mol = answer in atoms

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

Atom to Mass Conversions Amt. of substance x 1mol x molar mass(g) given in atoms 6.022x1023atom 1 mol =answer in mass (g)

What is the mass in grams of 1.50x1023atoms of tin?