Chapter 2 cont’ Atoms and Elements Recall: Atomic Number Number of protons Z Mass Number Protons + Neutrons Whole number A Abundance = relative amount (in %) found in a sample

Reacting Atoms when elements undergo chemical reactions, the reacting elements do not turn into other elements ◦ Dalton’s Atomic Theory since the number of protons determines the kind of element, the number of protons in the atom does not change in a chemical reaction however, many reactions involve transferring electrons from one atom to another 2

Charged Atoms when atoms gain or lose electrons, they acquire a charge charged particles are called ions when atoms gain electrons, they become negatively charged ions, called anions (Cl - ) when atoms lose electrons, they become positively charged ions, called cations (Na + ) ions behave much differently than the neutral atom ◦ e.g., The metal sodium, made of neutral Na atoms, is highly reactive and quite unstable. However, the sodium cations, Na +, found in table salt are very nonreactive and stable 3

Ionic Charge from Group Numbers Ionic Charge from Group Numbers The charge of a positive ion is equal to its Group number. Group 1A(1) = 1+ Group 2A(2) = 2+ Group 3A(3) = 3+ The charge of a negative ion is obtained by subtracting 8 or 18 from its Group number. Group 6A(16) = = 2- or = 2- 4

Atomic Structures of Ions Nonmetals form anions For each negative charge, the ion has 1 more electron than the neutral atom ◦ F = 9 p + and 9 e -, F ─ = 9 p + and 10 e - 5 Metals form cations For each positive charge, the ion has 1 less electron than the neutral atom Na atom = 11 p + and 11 e -, Na + ion = 11 p + and 10 e -

Examples Predict the charge and identify the number of proton and electron from that ion ◦ Mg  ◦ Al  ◦ O  ◦ P 

Collection Terms A collection term states a specific number of items. 1 dozen donuts = 12 donuts 1 ream of paper = 500 sheets 1 case = 24 cans 2 In chemistry, how do chemists know the number of atoms in an element or compound?

A Mole of Atoms A mole is a unit of measurement used in chemistry to express amounts of a chemical substance, the same number of particles as there are carbon atoms in 12.0 g of carbon. a collection term “dozen” 3 Avogadro’s Number = x mole = N A = x of anything

Relationship Between Moles and Mass The mass of one mole of atoms is called the molar mass The molar mass of an element, in grams, is numerically equal to the element’s atomic mass, in amu 9 E.g 1 H atom = 1.01 amu 1 mol H = 1.01g x atoms of H = ???? g

Examples Give the molar mass for each A. 1 mole of Li atoms =________ g B.1 mole of Co atoms =________g C.1 mole of S atoms= ________g 10

Converting between mass, moles and atoms g C mol C g C mol C atoms

Examples Assuming all pennies are pure copper and each has a mass of 2.5 g ◦ Without doing calculation, determine the number atoms of copper present in 1 mole ◦ How many pennies does it take to make a mole?

Examples In a 3.0 moles of O 2 molecules ◦ How many oxygen molecules are there ? ◦ How many oxygen atoms are there? Calculate the moles of carbon in g of pencil lead Calculate the mass (in grams) of moles of titanium