Midterm Review

1
Midterm Review

• Topic 1
• The Atom

2
Vocabulary

• Atom
• Atomic mass
• Atomic mass unit
• Atomic number
• Compound
• Electron
• Element
• Excited state
• Ground state
• Heterogeneous
• Homogeneous
• Isotope
• Mass number
• Mixture
• Neutron
• Orbital
• Proton
• Pure substance
• Wave-mechanical model

3
Daltons Atomic Theory

• All elements are composed of identical atom.
• All atoms of a given element are identical.
• Atoms of different elements are different that
  is, they have different masses.
• Compounds are formed by the combination of atoms
  of different elements. (Law of multiple
  proportions)

4
Parts of the Atom

• Electron
• J.J. Thomson
• Smallest unit of the atom
• Negativity charged
• Plum Pudding model

5
Parts of the Atom

• Nucleus
• Ernest Rutherford
• Gold Foil Experiment
• Alpha Particles
• If the Plum Pudding model was correct then the
  a particles would pass through the foil with just
  a few being slightly deflected.
• Some of the a particles were deflected, and some
  even bounced back.
• Rutherford concluded that atoms have a small
  dense positively charged central core, and the
  rest is mostly empty space

6
Modern Atomic Theory

• The Bohr Model
• Proposed a model of the atom that showed that
  atom with a dense nucleus with electrons found in
  surrounding orbits
• He proposed that electrons requires a specific
  amount of energy to stay in each orbit
• He suggested that the first orbital could hold
  only 2 electrons and that the 2nd orbital could
  hold 8 e-

7
Modern Atomic Theory

• The Wave-Mechanical Model
• Electrons have properties for both waves and
  particles
• The major difference between the Bohr model and
  the Wave-Mechanical Model is the way that the
  electrons are pictured.
• Instead for moving in fixed orbits, the electrons
  move in areas called orbitals.
• Orbital is described as a region in which an
  electron of a particular amount of energy is most
  likely to be found.

8
Modern Atomic Theory

• The Modern model of the atom has been developed
  over a long period of time

Wave-mechanical
Bohr
Rutherford
Thompson
Dalton
9
Subatomic Particles

• Because the mass of a proton is so small, it is
  more convenient to use a different scale whose
  units are called atomic mass units.

10
Subatomic Particles

• Each atom of a specific element must contain the
  same number of protons as each other atom of the
  same element
• The number of protons in the nucleus of the atoms
  is the atomic number of that element.
• For example The atomic number of Chlorine is 17
  so therefore each atom of Chlorine contains 17
  Protons

11
Subatomic Particles

• Mass Number
• The nucleus of the carbon atoms, containing 6
  protons and 6 neutrons is taken as the standard
  mass.
• The sum of the number of protons and the number
  of neutrons is called the mass number

12
Isotopes

• All atoms of a given elements contain the
  same number of protons, but the number of
  neutrons can vary.
• When the number of neutrons vary, then the mass
  of then atoms will be different.
• These different forms of an atom are
  called isotopes.
• Isotopes are atoms of the same element that have
  different numbers of neutrons

13
Isotope Symbols
Nuclear symbol
14
Atomic Masses

• This is the number that is found on the periodic
  table.

15
Location of Electrons

• Energy levels
• The orbitals in an atom form a series of energy
  levels in which electrons may be found.
• Each electron in an atom has its own distinct
  amount of energy that corresponds to the energy
  level that it occupies.
• Electrons can gain or lose energy and move to
  different energy levels
• Electrons can absorb only distinct, or fixed
  about of energy that allows it to move to a
  higher energy level.

16
Excited and Ground State

• When the electrons occupy the lowest available
  orbitals, the atom is said to be in the ground
  state.
• When electrons are subjected to stimuli such as
  heat, light, or electricity, an electron may
  absorb energy and temporally move to a higher
  energy level
• This unstable condition is called an excited
  state.

17
Excited State

• The electron quickly returns to a
  lower available energy level,
  emitting the same amount of energy it absorbed to
  go to the higher energy level.
• This admission of energy can be seen with an
  instrument called a spectroscope.

18
Atomic Spectra

• Each element has its unique atomic spectra.
• These spectra can be used to identify elements

19
Electron Arrangements

• Although the electrons in an atom contribute
  little to the mass of an atom, their arrangement
  determines its chemical properties.
• The chemical properties of an element are
  based on the number
  of valance electrons, or outer
  most electrons.

20
Orbitals and Electron Capacity of the First Four Principle Energy Levels Orbitals and Electron Capacity of the First Four Principle Energy Levels Orbitals and Electron Capacity of the First Four Principle Energy Levels Orbitals and Electron Capacity of the First Four Principle Energy Levels Orbitals and Electron Capacity of the First Four Principle Energy Levels
Principle energy level (n) Type of sublevel Number of orbitals per type Number of orbitals per level(n2) Maximum number of electrons (2n2)
1 s 1 1 2
2 s 1 4 8
2 p 3 4 8
3 s 1 9 18
3 p 3 9 18
3 d 5 9 18
4 s 1 16 32
4 p 3 16 32
4 d 5 16 32
4 f 7 16 32
21
Electron Configuration

• Follow the following rules to write and electron
  configuration
• Each added electron is placed into the sublevel
  of lowest available energy level
• No more that two electrons can be placed in any
  orbital
• A single electron must be placed into each
  orbital of a given sublevel before any pairing
  takes place (Empty Bus seat Rule)
• The outermost principle energy level can only
  contain electrons in the s and p orbitals

22
Orbital Notation

• While electron configuration notation can be
  useful, it does not show how the electrons are
  distributed in each sublevel

23
Types of Matter

• Some matter looks uniform and doesnt seem to be
  made up of parts.
• When an material had uniform composition
  throughout, the sample is said to be homogeneous.
• It can contain more that one type of particle,
  but particles are evenly mixed

24
Types of Mater

• Other materials are obviously made up of parts.
• Such materials, which have varying compositions,
  are said to be heterogeneous
• They are made up of parts with different chemical
  and physical properties.
• These parts are not uniformly mixed or dispersed

25
Types of Matter

• Matter can be divided into major categories
• Pure substances
• All pure substances are homogeneous
• Mixture
• Can be either homogeneous or heterogeneous

26
Pure Substance

• A sample is a pure substance id its composition
  is the same throughout the sample.
• There are two types of pure substances
• Element
• Compound

27
Element

• Elements are substance that cannot be broken down
  or decomposed into simpler substances by chemical
  means.
• There are 91 naturally occurring elements
• The elements are arranged on the periodic table
  of elements

28
Compound

• Compounds are composed of two or more elements
  that are chemically combined in definite
  proportions by mass.
• Although all compounds contain at lease 2
  different types of atoms, the composition of the
  compound is the same throughout.
• The Law Of Definite Proportions

29
Mixture

• A mixture is a combination of two or more pure
  substances that can be separated by physical
  means

30
Distinguishing between Mixtures and Compounds