CHAPTER 4 ATOMIC STRUCTURE

Aristotle (Greek) Thought all substances were built from either fire, earth, air, water Thought that atoms of a liquid are smooth and round Thought atoms of a solid were rough and prickly

Dalton’s Atomic Theory (1766) Evidence for atoms Measured the masses of elements Compounds have fixed composition All matter is made up of individual particles called atoms, which cannot be divided

1All elements are composed of atoms 2All atoms of the same element have the same mass, and atoms of different elements have different masses 3compounds contain atoms of more than 1 element 4in a particular compound, atoms of different elements always combine the same way

Evidence for subatomic particles –Mass and charge are spread throughout the atom –Earnest Rutherford- ( ) Alpha particles---fast moving positive charged All the atoms positive charge is in the nucleus The nucleus is the positively charged mass located in the center of the atom Ques.1-5 pg. 105

SECTION 4-2 Properties of subatomic particles Protons-- + charged particles, varies among elements Each nucleus contains at least one positively charged particle +charge = proton

Electron - charge 1- Found outside the nucleus in an electron cloud or (shell)

Neutron No charge Found in the nucleus Mass almost = to a proton Protons, electrons and neutrons can be distinguished by mass, location in an atom and the charge

ATOMIC NUMBER AD MASS NUMBER The atoms of any element contain the same number of protons Example there is one proton in the nucleus of every hydrogen atom. There hydrogen has an atomic number of 1 ATOMIC NUMBER = NUMBER OF PROTONS

Atoms of different elements have different numbers of protons Sulfur= atomic #= 16 because it has 16 protons in the nucleus Each positive charge is balanced by a negative charge SO hydrogen has 1 proton and 1 electron sulfur 16 protons and 16 electrons

MASS NUMBER= the sum of the protons and neutrons in the nucleus of the atom Ex Aluminum= 13 protons+14 neutrons= an atomic mass of 27 Number of neutrons= mass#-atomic number Ex. Aluminum 27-13= 14 (#of neutrons)

ISOTOPES When an atom does not have the same number of neutrons Same atomic number but different mass #’s Ex. Oxygen-16, 17, and 18 All oxygen atoms have 8 protons, but some have 9 or 10 neutrons Ques. 1-7 pg. 112

Energy levels 1 one orbital max 2 electrons 2 four orbitals max 8 electrons 3 nine orbitals max 18 electrons 4 sixteen orbitals max 32 electrons

Electron configuration—arraignment of electrons in the orbitals of an atom Lowest levels get filled before higher energy levels----inner to outer Stable electron configuration is the one in which the electrons are in orbitals with the lowest possible energies (ground state) Ques. 1-5 pg. 118

4-3 Modern Atomic Theory Niels Bohr Danish physicist focused on electrons in the electron cloud Energy levels Each electron has a fixed amount of energy Electrons closer to the nucleus have less energy than further away from the nucleus

They move in a less than predicable way Atomic orbitals –The electron cloud represents all the orbitals in an atom –An orbital is a region of space around the nucleus figure 15 page 117 (copy into notes) –Draw in your notes the Thomson, Rutherford, Bohr, and electron cloud models (pg 115)

An electron in an atom can move between energy levels when the atoms gain or lose energy The size of the jump between orbitals determines the amount of energy gained or lost

Evidence for movement from one level to another is light---light is a form of energy--- --heat is another cause of movement of electrons from one orbital to another Electron cloud-how electrons behave in their orbitals Electrons move like planets in the solar system around the nucleus, they move in a less than predicable way

When electrons move to a higher energy level they are considered in an excited state Ex. He, Ne, Ar Kr, Xe find out the names of these elements Page 118 questions 1-5