Atoms and Elements Structure of an Atom Charges

Atoms and Elements

Structure of an Atom Charges • Electron – negative • Proton – positive • Neutron - neutral Parts • Nucleus – neutrons & protons • Orbitals - electrons

Elements • Pure chemical substances made up of one type of atom • Building blocks of matter • Over 115 elements known - and more being discovered

Elements – Symbol / Name Symbol: one or two letter abbreviation Examples: C Carbon O Oxygen Mg Magnesium Br Bromine Au Lb K Na Latin Gold-aurum Lead-plumbum Potassium-kalium Sodium-natrium

Elements – Atomic Number DEFINES the element Atoms are neutral… so have same # electrons (-) as protons (+) • ALL Carbon atoms have six protons, and …ALL atoms with six protons are Carbon • BUT… they can have different numbers of neutrons These are called isotopes of carbon

Elements – Atomic Mass Calculated from Mass Number • MASS NUMBER = mass of all particles in one atom (protons, neutrons and electrons) • Measured in “atomic mass units” (amu)

Elements – Mass Number • MASS NUMBER = mass of all particles in one atom (protons, neutrons and electrons) • Mass of 1 proton = 1 amu Mass of 1 neutron = 1 amu Mass of 1 electron = really, really tiny! • SO… mass number = # protons + # neutrons Carbon • 6 protons x 1 amu/proton = 6 amu • 6 neutrons x 1 amu/neutron = 6 amu • 6 electrons x really tiny mass = 0 amu TOTAL = 6 amu + 0 amu = 12 amu

Elements – Mass Number Nitrogen Helium Atomic Number = 2 (protons) Atomic Number = 7 (protons) Mass Number = 4 amu (p + n) Mass Number = 14 amu (p + n)

Elements – Atomic Mass • BUT… Why is the atomic mass for Lithium (atomic number 3; with 3 protons) = 6. 94? !? ! NOTE: Mass number is used • …. Isotopes to name isotope Lithium-6 - 3 protons, 3 neutrons - mass number = 6 - 7. 5% of all lithium Lithium-7 - 3 protons, 4 neutrons - mass number = 7 - 92. 5 % of all lithium

Elements – Atomic Mass • BUT… Why is the atomic mass for Lithium (atomic number 3; with 3 protons) = 6. 94? !? ! • Calculation: Weighted Average (info. only): – 7. 5 % Lithium-6 at 6 amu – 92. 5 % Lithium-7 at 7 amu • (0. 075 x 6 amu) + (0. 925 x 7 amu) = (0. 45 amu) + (6. 48 amu) = 6. 93 amu

Elements – Atomic Mass • The atomic mass of an element is calculated by doing a weighted average of the mass numbers of all naturally existing isotopes. • If you round the atomic mass of an element to the nearest whole number, you get the mass number of the most common isotope. 7. 0

Elements – Symbol / Name Same # protons, different # neutrons Atomic Mass • “Average” for all carbon • Calculated from mass numbers of isotopes • On the periodic table All have same # protons Mass Number • Calculated for each individual isotope • Used to name the isotope • Averaged together to represent all carbon

Elements - SUMMARY

Structure of an Atom • Outside the nucleus electron – Electron • Atomic mass • Charge nucleus (containing protons and neutrons) 0 (-)

Structure of an Atom • Electrons are arranged in orbits – Orbit 1 holds 2 electrons – Orbit 2 holds 8 electrons – Orbit 3 holds 8 electrons…

Structure of an Atom • Nucleus – the center of an atom contains… – Protons • Atomic mass • Charge 1 (+) – Neutrons • Atomic mass • Charge 1 none

Symbols • Either 1 or 2 letters symbols – First letter Capital, second lower case – Some based on Latin name Example Latin C Carbon Au Gold-aurum O Oxygen Lb Lead-plumbum Mg Magnesium K Potassium-kalium Br Bromine Na Sodium-natrium

The Periodic Table • Elements are arranged by size and chemical properties. • Rows – Period • Size • Columns – Group • Properties

Properties • Properties are related to atomics structure. • The number of electrons in the outer most orbit (valence electrons) determine how an atom will behave in chemical reactions.