HISTORY OF THE ATOM 460 BC Democritus develops the idea of atoms He pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMOS (greek for indivisible)

HISTORY OF THE ATOM SCIENTISTMODEL OF THE ATOM MAJOR CONTRIBUTIONS & POINTS DALTON (1803) AKA: Billard Ball model Matter is made of small particles called atoms. 1. Atoms are indestructible. They cannot be created or destroyed during chemical or physical changes. 2.Atoms of an element are identical. They have the same mass. 3.Atoms of different elements have different masses. 4.Compounds are formed by combining atoms of different elements.

8 X 2 Y 16 X8 Y + 2.1

HISTORY OF THE ATOM SCIENTISTMODEL OF THE ATOM MAJOR CONTRIBUTIONS & POINTS THOMPSON (1890’s) AKA: plum pudding model discovers electrons (negative charge) electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron’s charge electrons

HISTORY OF THE ATOM SCIENTISTMODEL OF THE ATOM MAJOR CONTRIBUTIONS & POINTS RUTHERFORD (1909) Gold foil experiment – alpha (+) particles were fired at Au foil: Results: KNOWTHIS!!! 99% alpha particles went straight thru, 1% were deflected. Findings: 1. Atom has a small, positively charged center. 2. Atom is mostly empty space with negatively charged electrons revolving around the outside FYI ONLY….If the atom is the Ralph Wilson Stadium Then the nucleus is a marble on the 50 yard line (1909 Nobel Prize in Chemistry)

2.2 Results: 99% of the alpha particles went straight thru, 1% were deflected swf Be able to explain and summarize Rutherford’s Gold Foil Experiment

HISTORY OF THE ATOM SCIENTISTMODEL OF THE ATOM MAJOR CONTRIBUTIONS & POINTS BOHR (1913) AKA: Planetary model electrons move in definite, fixed orbits around the nucleus each orbit only able to contain a set number of electrons.

Bohr’s Atom- electrons move in definite, fixed orbits around the nucleus electrons in orbits nucleus

HISTORY OF THE ATOM SCIENTISTMODEL OF THE ATOM MAJOR CONTRIBUTIONS & POINTS QUANTUM MODEL (1930’s) AKA: Wave Mechanical or Electron cloud model Electrons have a distinct amount of energy and have wave-like properties. They travel in regions called orbitals. These regions are the most likely location of an electron.

HISTORY OF THE ATOM reviewed Atomos song TwAiBUAtomos song TwAiBU Crash Course Science Classroom

Atoms The basic unit of Matter The smallest particle of an element that retains the properties of that element. Made up of subatomic particles

ATOMIC STRUCTURE All About Atoms All About Atoms Particle Proton Neutron electron Charge + charge - charge No charge 1amu 1/1836 Mass

ATOMIC STRUCTURE Represents the number of protons in an atom Never changes P+ equal to the number of e- the number of protons and neutrons in an atom Neutrons equal mass # - atomic # He 2 4 Mass Number Atomic number number of electrons = number of protons

HELIUM ATOM + N N proton electron neutron Shell What do these particles consist of?

Isotopes Atoms with the same atomic number but different mass number or Atoms having the same number of protons but different numbers of neutrons Which atom is an isotope of oxygen? 1). O 2). O 3). O Isotopic notation: O or O

2.3

2. How many protons, neutrons, and electrons are in C 14 6 ? 3. How many protons, neutrons, and electrons are in C 11 6 ? 6 protons, 8 (14 - 6) neutrons, 6 electrons 6 protons, 5 (11 - 6) neutrons, 6 electrons CHEM DO… Do You Understand Isotopes? 1. Define an isotope 2.3 Isotope Maker

Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons # OF NEUTRONS = mass number – atomic number X A Z H 1 1 H (D) 2 1 H (T) 3 1 U U Mass Number Atomic Number Element Symbol 2.3

Average Atomic Mass Average Atomic Mass of an element is the weighted average of an element’s naturally occurring isotopes. What is the average mass of cesium given the percent abundance of selected cesium isotopes? 75% Cs % Cs % Cs- 134

Practice Guide pages 3 and 4 show work set up and solve

Bohr Model of the Atom (planetary model) Energy Levels Electrons revolve around the nucleus in one of several orbits/shells/ principal energy levels Principal energy level (PEL) is the same as the period number on the periodic table There are 7 PEL’s therefore 7 periods PEL is designated by a quantum number (n)

Period Group Alkali Metal Noble Gas Halogen Alkali Earth Metal 2.4

Location of electron According to the Bohr model, electrons are found in shells around the nucleus first shell maximum of 2 electrons second shell maximum of 8 electrons third shell max of 18 electrons fourth shell max of 32 electrons

ATOMIC STRUCTURE There are two ways to represent the atomic structure of an element or compound; 1. Electronic Configuration 2. Electron dot diagrams

ELECTRONIC CONFIGURATION With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example; N Nitrogen in 1 st shell 5 in 2 nd shell configuration = 2, = 7

ELECTRONIC CONFIGURATION Write the electronic configuration for the following elements; Ca O Cl Si Na B 11 5 a)b)c) d)e)f) 2,8,8,22,8,1 2,8,72,8,42,3 2,6

Valence Valence shell is outermost occupied energy level and is the same as the period number in the periodic table Valence electrons are the electrons in the outer energy level of an atom

DOT & CROSS DIAGRAMS With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. For example; Nitrogen N XX X X XX X N 7 14

DOT & CROSS DIAGRAMS Draw the Dot & Cross diagrams for the following elements; O Cl a)b) O X X X X X X X X Cl X X X XX X X X X X X X X X X X X X

An ion is an atom, or group of atoms, that has a net positive or negative charge. cation – ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. anion – ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Na 11 protons 11 electrons Na + 11 protons 10 electrons Cl 17 protons 17 electrons Cl - 17 protons 18 electrons 2.5

13 protons, 10 (13 – 3) electrons 34 protons, 36 (34 + 2) electrons Do You Understand Ions? 2.5 How many protons and electrons are in Al ? 3+3+ How many protons and electrons are in Se ?

A monatomic ion contains only one atom A polyatomic ion contains more than one atom 2.5 Na +, Cl -, Ca 2+, O 2-, Al 3+, N 3- OH -, CN -, NH 4 +, NO 3 -

SUMMARY 1. The Atomic Number of an atom = number of protons in the nucleus. 2. The Atomic Mass of an atom = number of Protons + Neutrons in the nucleus. 3. The number of Protons = Number of Electrons. 4. Electrons orbit the nucleus in shells. 5. Each shell can only carry a set number of electrons.