Atomic Calculations CPS Chemistry

Parts of the atom…  Electron Negative Charge Allows atoms to bond & react 9.1x kg

 Neutron Neutral Charge, number can vary in nucleus Binds nucleus together 1.7x kg

 Proton Positive Charge unique number, gives atoms/element their identity 1.7x kg

Atomic Number  A unique number which is equal to the number of protons in the nucleus (whole number) of an element Examples  Hydrogen – 1  Lithium – 3  Oxygen - 8

Isotopes  Isotopes are when there are varying numbers of neutrons in the nucleus for a type of element  Example for hydrogen Protium – 1Proton, 0 Neutrons Deuterium – 1Proton, 1 Neutron Tritium – 1 Proton, 2 Neutrons  Nuclide – a general term for any isotope of an element

Atomic Mass  The atomic mass is the sum of the masses of the protons and neutrons in the nucleus of a atom – electrons are not counted because their relative mass is insignificant compared to the other two subatomic particles.

 The atomic mass is usually expressed as a decimal because it is an average of the masses of all the isotopes for that element

How many neutrons?  If the atomic number is the number of protons in an element, and the atomic mass (round to the nearest whole number) is the number of protons + neutrons than to find the number of neutrons… Atomic Mass – Atomic Number = # of Neutrons

Example  If the atomic number for silver (Ag) is 47, and the atomic mass is 108, how many neutrons are there? Atomic # = 47 Atomic Mass = = 61 neutrons

How many electrons are there?  In a neutral atom, the number of electrons equals the number of protons  If there is a +1 next to an atom, it means that it has one less electron than protons  If there is a -1 next to an atom, it means that it has one more electron than protons

Example 2  Find the number of subatomic particles associated with Sn +2  On the periodic table of elements Tin has an atomic number of 50, and an atomic mass of 119  Number of protons = 50 Number of neutrons = 69 Number of electrons = 48

Calculating Atomic Mass of Molecules  When you add the atomic mass of two particles together, you get the atomic mass of the molecule.  You can have more than one of any atom, so you need to multiply the mass times that number.

Ex. CO is Carbon Monoxide Carbon has an atomic mass of 12 Oxygen has a mass of 16 The total mass for the molecule is  12+16= 28g

What about More than One of an atom?  If there are more than one atom of a given kind, multiply that subscript number by the atoms mass.  Then add the total of all the atoms.

Examples: H2O Multiply the hydrogen by 2 then add it to the oxygen.  (Hx2)+O=  (1x2)+16=18g C6H12O6  (Cx6)+(Hx12)+(Ox6)=  (12x6)+(1x12)+(16x6) =180g

The Mole: more than just a furry little creature…  It is a unit of measure, since atoms are very, very, very small a better way to count atoms so the unit is the mole  The mole is equal to 6.022x10 23 also called Avogadro’s number  1 mole of a element = atomic mass of that element

Grams to moles Take the given number of grams and multiply it by 1 mole over the atomic mass. Example: How many moles is contained in a 72g sample of magnesium? 72 g of Mg x 3 mol 1 mol = 24 g

Moles to grams Take the given number of grams and multiply it by atomic mass over 1 mole Example: How many grams are there in a 1.5 mole sample of sulfur? 1.5 mol x = 48 grams 32 g 1 mol

Atoms to moles & moles to atoms  To calculate the number of moles in a amount of atoms, divide by Avogadro's number  To calculate the number of atoms in a sample, first convert to moles, then multiply by Avogadro's number

Island of Instability… There are 92 naturally occurring elements But scientists can make elements in the lab, the current “prize” is to make & stabilize element 114…make & stabilize element 114