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Unit 3: The Atom.

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1 Unit 3: The Atom

2 Evolution of the Structure of an Atom

3 Dalton’s Atomic Theory
All elements are composed of indivisible particles called atoms Atoms of the same element are identical. The atoms of any one element are different from those of any other element. Atoms of different elements can physically mix together or chemically combine with one another in simple whole number ratios to form compounds.(law of definite composition) Chemical rxns occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.(law of conservation of mass)

4 J.J. Thomson discovered the electron plum pudding model

5 Rutherford discovered the nucleus
Proposed electrons surround the nucleus in a cloud

6 Bohr Models Electrons are at specific distances from the nucleus of an atom in energy levels Energy Level 1 2 3 4 # ELECTRONS

7 Quantum Mechanical Model
The modern description of electrons in atoms proposed by Schrödinger

8 Quantum Mechanical Model
proposed that the location and energy of an electron could be determined by the Schrödinger wave equation

9 Quantum Mechanical Model
This model tells you that the electron is found 90% of the time within a cloud

10 The Atom Today The atom is the smallest particle of an element that retains the properties of that element Atoms can only be seen with proper instrumentation Dalton’s Atomic Theory wasn’t completely correct Atoms can be broken down into subatomic particles Atoms of the same element are not identical

11 Properties of Subatomic Particles

12 Distinguishing Between Atoms

13 Atomic Number Number of protons in the nucleus of an atom Identifies the element Elements are listed on periodic table according to atomic number

14 Atomic Number

15 Atomic Number

16 Atomic Number atoms are electrically neutral # protons = # electrons

17 Mass Number total number of protons and neutrons in an atom It is not found on the periodic table but can be estimated

18 Shorthand Notation

19 Fill in the following table

20 Ions Atoms with a charge Cations – positive ions that lost electrons Anions – negative ions that gained electrons

21 Isotopes Atoms that have the same number of protons but different numbers of neutrons Differ in their mass number

22 Isotopes the existence of isotopes was not predicted by Dalton, who said atoms of the same element are the same

23 Isotopes identified by their mass # , write the name of the element then a hyphen with the mass number

24 Isotopes

25 Uses of Isotopes C-14 = archeological carbon dating Am-241 = smoke alarms I-131 = treating thyroid disorder Co –60 = cancer treatment

26 Atomic Mass (atomic weight)
weighted average mass of all the atoms in naturally occurring samples of the element

27 Atomic Mass reflects the mass and the relative abundance of isotopes as they occur in nature

28 Atomic Mass To calculate the atomic mass of an element multiply the atomic mass of each isotope of the element by its relative abundance, then add the results atomic mass = mass1rel.abd.1 + mass2rel.abd.2+...

29 1. Calculate the % abundance of fictitious element Nv 2
1. Calculate the % abundance of fictitious element Nv 2. If the mass of 293Nv is amu (red)and that of 295Nv is amu (blue), what is the atomic mass of Nv? .

30 Quantum Mechanical Model

31 Quantum Mechanical Model and Atomic Orbitals
Principle Quantum Number (n) designates energy levels by n=1,2,3,4….as the electrons move away from the nucleus

32 Quantum Mechanical Model and Atomic Orbitals
Sublevels are found within each energy level and they are designated by s, p, d, and f

33 Quantum Mechanical Model and Atomic Orbitals

34 Quantum Mechanical Model and Atomic Orbitals
Atomic orbitals make up each sublevel

35 Quantum Mechanical Model and Atomic Orbitals
Each Atomic orbital holds 2 electrons

36 Quantum Mechanical Model and Atomic Orbitals
Chart

37 Electron Configuration
The way electrons are arranged around the nucleus of an atom according to the quantum mechanical model Represented by orbital notation

38 Electron Configuration
Guidelines: 1. Aufbau Principle Electrons enter orbitals of lowest energy first

39

40

41 Electron Configuration
2. Pauli Exclusion Principle An atomic orbital at most describes 2 electrons, and they must be of opposite spin

42 Electron Configuration
2. Pauli Exclusion Principle

43 Electron Configuration
3. Hund’s Rule When electrons occupy orbitals of the same energy, one electron occupies each orbital until all electrons are of the same spin, then second electrons can be added

44 Electron Configuration
3. Hund’s Rule

45 Electron Configuration
Exceptions to the rules Cu and Cr

46 Electron Configuration
Shorthand Notation Energy level (n=1,2,3,…) symbol for sublevel (s, p, d, f) Superscript for electrons Superscripts sum = total electrons

47 Electron Configuration

48 Electron Configuration
Noble Gas Notation Previous noble gas symbol in brackets Additional orbitals in shorthand

49 Electron Configuration
Noble Gas Notation

50 Review Write the electron configuration for Sulfur in orbital, shorthand, and noble gas notation.

51 Review Write the electron configuration for Chromium in orbital, shorthand, and noble gas notation.

52 Review Dalton Thompson Rutherford Bohr Schrodinger

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