STUDYING ATOMS Ch. 4.1

TrueFalseStatementTrueFalse Daltons atomic theory said all matter is made of atoms, which can be divided Thomson’s atomic model, showed that atoms are even smaller than thought Rutherford’s atomic model showed that the positive charge is contained in the nucleus Thomson’s model is also called the plum pudding model Rutherford was the 1 st to propose an atomic theory

Greek Atom years ago  Democritus- Greek philosopher  Atom from atomos – uncut, indivisible  Different types of atoms with different properties  Aristotle's Model :

Dalton’s Atomic Theory- 1800’s  Evidence  Measured masses of compounds  Found that the ratio of masses of the elements in a compound is always the same  Fixed composition!  Theory  All elements are composed of atoms  All atoms of the same element have the same mass, and atoms of different elements have different masses  Compounds contain atoms of more than 1 element  In a particular compound, atoms of different elements always combine in the same way

Dalton Summed Up:  All matter is made of individual particles, called atoms, which cannot be divided!

Thomson’s Experiment  Glass tube without air  1 side positive, 1 side negative  Glowing beam appears in middle

Thomson’s Model of the Atom-1870’s  Evidence  Negative charge attracted to positive charge  1 st evidence atoms are made of even smaller particles  Model  Atom = neutral  Negative and positive evenly mixed  Called Plum Pudding after English dessert

Rutherford’s Experiment  Aimed alpha particles at gold screen  Screen flash when struck by alpha particle  Traced path of alpha particles

Rutherford’s Atomic Theory-1900’s  Evidence  Alpha particles- fast moving positive charge  Positive is not evenly spread  Nucleus- dense, positively charged mass at atoms center  Theory  All of an atoms positive charge is concentrated in the nucleus

THE STRUCTURE OF AN ATOM Ch. 4.2

TrueFalseStatementTrueFalse Isotopes have the same atomic #, but different masses due to protons The atomic # equals the # of protons in the element The mass # is the sum of the protons and electrons Protons and neutrons have almost identical masses Protons, neutrons and electrons are subatomic particles of the atom

Subatomic Particles  Protons- Rutherford  Positively charged particle found in the nucleus  Same as atomic #  Electrons- Thomson  Negatively charged particle found outside the nucleus  Atomic # - charge  Neutrons- Chadwick  Neutral particle found in nucleus  Mass almost exact to the proton  Mass # - Atomic #

Comparing Subatomic Particles ParticleSymbolChargeRelative Mass Actual Mass Electrone-1-1/ x Protonp x Neutronn x Proton and neutrons= same ________

Atomic Number  Atoms of any given element always have the same # of p+  Every p+ is balanced by e- for a neutral charge  = # of e- in an atom of that element  = the # of p+ in an atom of that element  Because atoms are neutral!

Mass Number  = p+ + n  Ex: Al  13 p+  14 n  Mass # = 27  n = mass # - atomic #  Ex: Al  Mass # = 27  Atomic # = 13  n=

Practice SymbolAtomic #Mass #ProtonsElectronsNeutrons Na2312 K P O W

Isotopes  Every element does have the same # of protons and electrons  Neutrons can vary  Have the same atomic #, but different mass # due to neutrons

Practice SymbolAtomic #Mass #ProtonsElectronsNeutrons Be Be Cl Cl -1 Na +3

MODERN ATOMIC THEORY Ch. 4.3

TrueFalseStatementTrueFalse Bohr’s model focused on electrons, and was adapted from Thomson Electrons can jump energy levels by gaining or losing energy Electron clouds are the likely areas in which you can find electrons The higher the energy the fewer the atomic orbitals; the lower the energy the higher # of orbitals Electron configuration is based on lettering the periodic table- s, p d, and e

Bohr’s Model  Partnered with Rutherford  Focused on electrons  Count the # of electrons, and place in orbit

Energy Levels  Energies that electrons can have  Electrons move levels when the atom gains or loses energy  Use with Bohr Models

Practice  B  Mg  Si  Ne

Electron Cloud Model  Improved Bohr Model  Visual model for most likely locations for electrons  Dense= electrons

Atomic Orbital's  Electron cloud = good approximation of how electrons behave in orbitals Energy Level# of OrbitalsMax # of Electrons

Electron Configuration  Arrangement of electrons in the orbitals  Most stable = electrons in orbitals with lowest energy  Ground State= all electrons have lowest energies

C= 1s 2 2s 2 2p 2 Cr= 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 4

Practice  Li  Mg  K

Lewis Dot Structures  Count valance electrons (outer layer of electrons)  Place around element, no more than 8

 Examples and rules for compounds Examples and rules for compounds

Practice  P  Be  Ca  CO2  HCl  NaCl