Atomic Structure Advanced Chemistry By PresenterMedia.com

Elements and Compounds Simplest form of matter Cannot be broken down into smaller stable state of matter Compounds Combination of elements in whole number ratios Can be broken down into smaller components

Every substance has unique physical and chemical properties Properties of Matter Physical Properties Chemical Properties Can be observed/measured without changing the composition. Examples are density, solubility and state of matter Intensive do not depend on amount (density and boiling point) Extensive do depend on amount (mass, volume) Can only be observed with a change in the composition Examples are rusting and flammability Every substance has unique physical and chemical properties

Changes in Matter Physical changes Change in a substance that results in different appearance but not composition Examples are bending and change in state of matter States of matter All particles in constant motion Solids have a definite shape and volume Liquids have a definite volume but not a definite shape Gases have neither a definite shape nor a definite volume Chemical changes (chemical reactions) Change in a substance that results in one or more new substances Indicators are smoke, heat, light, odor Initial materials are reactants; final materials are products

Laws of Chemistry These laws help to explain the behavior of atoms during chemical reactions (changes) Law of Conservation of Mass Matter cannot be created or destroyed but can change forms Law of Definite Proportions A chemical always has the same whole number ratio of elements to one another Law of Multiple Proportions Elements can combine in different whole number ratios to make different chemicals

Dalton’s Atomic Model True False All matter is composed of extremely small particles called atoms All atoms of a given element are identical, having the same size, mass and chemical properties. Atoms of specific elements are different from any other element Atoms cannot be created, divided, or destroyed Different atoms combine in small whole number ratios to form compounds Atoms are separated, combined, and rearranged in reactions True False

Atomic Structure Discovery Early experiments Thompson Cathode ray tube Discovered electrons (1st subatomic particle) Plum pudding model/chocolate chip cookie dough ice cream Rutherford Gold foil experiment Discovered nucleus Later discovered protons

Basic Atomic Structure Nucleus Central dense region of an atom with two subatomic particles Positively charge subatomic particle Protons Neutrons Subatomic particle without a charge Empty space surrounding the nucleus of an atom Electron cloud Electrons Negatively charged subatomic particle

Atomic Differences Atomic number Identifies the atom as a specific element Indicates the number of protons In a neutral atom, protons = electrons Mass number Indicates the number of protons and neutrons Atoms with same number of protons but different number of neutrons are isotopes Atomic mass number Weighted average of mass of all isotopes

Radioactivity Nuclear reaction involving a change to the atom Atom becomes more stable/less energy Radiation is emitted Alpha (a) particle– Helium nucleus Beta (b) particle – neutron splits Gamma (g) ray – energy released usually with an alpha or beta particle

Bohr Proposed energy states are involved with atoms Ground state is lowest energy for an atom Excited state is energy is gained by the atom Also proposed atomic orbitals Electrons travel around the nucleus Assigned quantum numbers to each energy level One is closest to the nucleus, then two, etc Electrons can move from energy level to energy level de Broglie – Wave Particle Duality Heisenberg Uncertainty Principle Impossible to know velocity and location of an electron at the same time

Atomic Orbitals Area around nucleus indicating location of electrons Principal quantum numbers/Energy levels Indicate size and energy of atomic orbitals Numbered from 1 to 7 Energy sublevels are found in the energy levels Are s, p, d, or f as determined by their shape (p. 133) Each sublevel has orbitals holding two electrons each s has one orbital p has three orbitals d has five orbitals f has seven orbitals Energy level 1 has 1 sublevel, 2 has 2 sublevels, 3 has three sublevels, 4 has 4 sublevels

Electron Configurations Arrangement of electrons in an atom Three rules define location Aufbau principle Electrons occupy lowest energy position (p. 138) Each orbital in a sublevel has the same energy Orbitals of different energy levels can overlap Pauli exclusion principle Electrons spin and in an orbital they are opposite Hund’s rule Negative charge plays a role in location One electron per orbital before a second one fills Exceptions are possible (d block)

Electron Configurations (cont) Notations Electron configuration notation Uses energy level, sublevel and number of electrons 1s2 2s2 2p3 is nitrogen Orbital diagram Box represents each orbital with energy level and sublevel written below it Electrons are represented with opposite arrows

Valence Electrons Electrons in the outermost energy level Determine the properties of an atom Determine position on periodic table Noble gases have full outer energy levels (most stable elements) Electron Dot Structures One dot for each valence electron Fill on sublevel at a time

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