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

• 1 All elements are composed of atoms• 2 All atoms of the same element have the

same mass, and atoms of different elements have different masses

• 3 compounds contain atoms of more than 1 element

• 4 in 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- (1871-1937)

• 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-1885-1962 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