CHEMISTRY 161 Chapter 2

MATTER ATOMS MOLECULES ELEMENTS John Dalton matter is composed of ‘building blocks’ MOLECULES ELEMENTS

an atom is the basic, undividable unit of any element Dalton’s postulates Elements are composed of small particles called atoms; atoms of an element are identical with same properties (mass) 2. Compounds are composed of atoms of more than one element; in a compound, the ratio of the number of atoms is an integer or fraction LAW OF DEFINITE PROPORTIONS 3. A chemical reaction involves separation and combination of atoms; atoms are neither created nor destroyed an atom is the basic, undividable unit of any element

1. Law of definite proportions 2. Law of conservation of mass in a chemical reaction no gain or loss of mass is observed unit of mass is g (gram) or kilogram (kg) each atom has a constant mass atomic mass – atomic weight

Structure of an Atom subatomic particles electrons protons neutrons

protons are a constituent of the nucleus proton,p 1.67262 × 10-27 kg +1.6022 × 10-19 C +1 electron,e 9.10939 × 10-31 kg -1.6022 × 10-19 C -1 m(p) / m(e) ≈ 1836 the atom’s positive charge is located in a small, dense central core ‘nucleus’ protons are a constituent of the nucleus

mass of the nucleus constitutes most of the mass of the atom + + + + + mass of the nucleus constitutes most of the mass of the atom 2. the nucleus is positively charged and contains protons 3. the nucleus constitutes only about 1/1013 space of an atom 4. electrons are as clouds around the nucleus

Neutron m(n) / m(e) ≈ 1838 m(n) > m(p) proton, p 1.67262 × 10-27 kg +1.6022 × 10-19 C +1 electron, e 9.10939 × 10-31 kg -1.6022 × 10-19 C -1 neutron, n 1.67493 × 10-27 kg 0 0 m(n) / m(e) ≈ 1838 m(n) > m(p)

Structure of an Atom subatomic particles electrons (‘cloud’) neutrons (nucleus) protons (nucleus) neutrons are the ‘glue’ of the nucleus

Atomic Number and Mass Number (PSE) mass number (number of protons plus neutrons) atomic number (number of protons) (number of electrons) in an atom, the number of electrons and protons are identical (charge neutrality)

ISOTOPES 6 neutrons 12 protons plus neutrons 6 electrons 6 protons elements with same number of electrons and protons but different number of neutrons ISOTOPES

Periodic Table of the Elements g r o u p

Periodic Table of the Elements metals nonmetals metalloids (semi metals) 8 main groups 10 transition metal groups metals lanthanides/actinides metals metals – shine, conduct electricity nonmetals – do not shine, do not conduct electricity metalloids – properties between metals and nonmetals

HOW HEAVY ARE ATOMS? CALCULATION

standard / calibration CHEMICAL MASS SCALE standard / calibration atomic mass unit (amu, u) one atom of carbon-12 12 u (exactly) we have to correlate u with kg

MOLE

one mole of a compound contains the same number of molecules/atoms as the number of atoms in exactly 12 g of 12C Avogadro’s number Na 6.023 x 1023

links micro and macroscopic world 6.023 x 1023 1 mole of H2O molecules 6.023 x 1023 atoms 1 mole of 12C 6.023 x 1023 atoms 1 mole of Na molecules 6.023 x 1023 1 mole of NaCl Avogadro’s number links micro and macroscopic world

formula mass: weight of one molecule H2O PSE O: 15.999 u H: 1.008 u H2O: 18.015 u formula mass: weight of one molecule correlation between u and kg

H2O O: 15.999 u H: 1.008 u H2O: 18.015 u 1 mole of H2O – 18.015 g Na 15.999 g/mol Na 1.008 g/mol Na 1.008 g/mol 1 mole of H2O – 18.015 g

CaO O: 15.999 u Ca: 40.08 u CaO: 56.08 u 1 mole of CaO – 56.08 g

2 H2 + O2 2 H2O STOICHIOMETRY 2 molecules 1 molecule 2 molecules 2 moles 1 mole 2 moles 4.03176g 31.9988g 36.03g x g y g 70.0g STOICHIOMETRY

2 H2 + O2 2 H2O STOICHIOMETRY 2 molecules 1 molecule 2 molecules 2 moles 1 mole 2 moles 4.03176g 31.9988g 36.03g x g y g 70.0g STOICHIOMETRY

How many grams of iron are in a 15.0 g sample of iron(III) oxide? Example I: How many grams of iron are in a 15.0 g sample of iron(III) oxide? 1. molecular formula Fe2O3 2. weight of one molecule 159.7 u 3. weight of one mole Fe2O3 159.7 g 4. 1 molecule Fe2O3 contains 2 atoms of Fe 5. 1 mole Fe2O3 contains 2 moles of Fe 159.7 g 111.69 g 15.0 g x g x = 10.5 g

How many atoms are in 10 kg of sodium? Example II: How many atoms are in 10 kg of sodium? 1 mole sodium = 22.98977 g 6.023 x 1023 atoms = 22.98977 g x atoms = 10,000 g x = 2.6 x 1026 atoms

How heavy are 1 million gold atoms? Example III How heavy are 1 million gold atoms? 1 mole gold = 196.96654 g 6.023 x 1023 atoms = 196.96654 g 1,000,000 atoms = x g x = 3.2 x 10-16 g = 0.32 fg

MOLE Avogadro’s number Na 6.023 x 1023