Chapter 4 Atomic Structure

4.1 Atoms Democritus (460 BC – 370 BC) first suggested the idea of atoms Indivisible and indestructible

Atoms The first model of the atoms was Dalton’s “All mater is made up of individual particles , which are indivisible”

Dalton’s Atomic Theory 1. All matter is made of atoms. Atoms are indivisible and indestructible.

Dalton’s Atomic Theory 2. All atoms of a given element are identical in mass and properties

Dalton’s Atomic Theory 3. Compounds are formed by a combination of two or more different kinds of atoms.

Dalton’s Atomic Theory 4. A chemical reaction is a rearrangement of atoms

Thomson’s Model Discovered electrons Often called the “Plum-Pudding” Model No mention of amount of electrons or their arrangement around the nucleus Revised Dalton’s theory to account for subatomic particles

Rutherford Model Discovered nucleus All of an atom’s positive charge is concentrated in its nucleus Electrons surround a dense nucleus Rest of the atom is empty space

Rutherford Model Known as the nuclear model The protons are located in the nucleus The electrons are around the nucleus The electrons occupy most of the volume of the nucleus

The Atom The smallest part of an element VERY SMALL

Atomic Structure Atoms can be broken down Protons Neutrons Electrons Every Element is different based on the number of each (individual personality)

Protons (p+) Positively Charged Each has a “+1” charge

Electrons (e-) Negatively charged Each has a “-1” charge

Neutrons (n0) No charge or “neutral” Mass = mass of proton

The Atomic Nucleus Most of the mass, little volume The central core of an atom Made of p+ and n0 Most of the mass, little volume Nucleus has a positive charge

The Atomic Nucleus Electrons orbit around nucleus like planets in the solar system Called the “electron cloud” Very little mass, lots of volume

How do we know the number of each elements p+ , e- , n0 Periodic Table is arranged by the element’s numbers

Hydrogen Name of Element Atomic Number Mass Number (round to the nearest whole number) 1 1.008 H Nuclear Symbol Hydrogen Name of Element

Atomic Number Amount of protons from one element to the next Ex: Oxygen atomic number = 8 because it has 8 protons

Atomic Number Since all elements start off as neutral …. The number of protons = number of electrons!

Mass Number Mass Number = protons + neutrons

Composition of an Element Use atomic number and mass number to determine composition # p+ = atomic # # e- = atomic # # n0 = mass # – atomic #

What can change in an atom Protons: can never change Electrons: if the number changes, then an ion is formed Neutrons: If the number changes, then an isotope is formed

IF the proton number changes… Then you have an entirely different atom

If the neutron number changes… Called an Isotope Mass number changes

If an atom gains electrons, then… The atom becomes negatively charged If an atom loses an electron, then… It becomes positively charged

Isotopes of Elements Protons never change, but the number of neutrons may vary

Isotopes Isotopes of the same element are the same except for # of n0 # of n0 vary so mass number changes

Isotopes Carbon-12, Carbon-14, Carbon-16 How many protons in each version of carbon? How many neutrons in each version of carbon?

Hydrogen Hydrogen has three known isotopes Hydrogen-1 (one proton, no neutrons) Hydrogen-2 (one proton, 1 neutron) Hydrogen-3 (one proton, 2 neutron)

4.3 Bohr’s Model Electrons arranged in circular paths around nucleus Orbit like planets n = energy level Only a certain amount of electrons can fit in each energy level

Bohr’s Model Electrons are located in energy levels with a fixed amount of energy

Energy Levels Each energy level can only hold 2 electrons Each energy level has “X” number of orbitals that can hold 2 electrons each Pauli Exclusion Principle Each orbital holds 2 electrons that spin in opposite directions

Maximum number of Electrons Energy Levels How many electrons fit in the 1st, 2nd, 3rd and 4th energy levels? Energy Level Number of Orbitals Maximum number of Electrons 1 2 4 8 3 9 18 16 32

Hund’s Rule When electrons occupy orbitals, one electron enters each orbital until all orbitals contain their max amount

Hund’s Rule Partially filled orbitals are much more stable than empty orbitals Example: Carbon has 6e- has 2e- in first orbital has 4e- in second orbital

Orbitals simplified Each energy level can hold 8 electrons except the first which holds 2 Fill in each level until