# 4.2 The Structure of an Atom

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4.2 The Structure of an Atom

Atomic Structure Atoms are composed of 2 regions:
Nucleus: center of atom that contains mass of atom Electron cloud: region that surrounds nucleus that contains most of space in atom Nucleus Electron Cloud

What’s in the Nucleus? Nucleus contains 2 of 3 subatomic particles:
Protons: subatomic particle w/ 1+ charge (p+) Rutherford Neutrons: subatomic particle w/ no charge (no) James Chadwick

What’s in the Electron Cloud?
The 3rd subatomic particle resides outside nucleus in electron cloud Electron: subatomic particle w/ 1- charge (e-) and virtually no mass JJ Thomson

How do these particles interact?
Protons and neutrons live compacted in tiny nucleus most atom’s mass electrons small and reside outside nucleus small mass (2000 e- = 1 p+ or no) occupy large volume of space outside nucleus Atoms

How do the subatomic particles balance each other?
In atoms: protons = electrons If 20 protons are present in atom then 20 electrons balance overall charge of atom—atoms are neutral The neutrons have no charge; therefore they do not need to (and often times don’t) equal protons or electrons

How do we know the number of subatomic particles in an atom?
Atomic #: indicates # of protons in atom Ex: Hydrogen’s atomic # is 1 hydrogen has 1 proton Ex: Carbon’s atomic # is 6 carbon has 6 protons **Number of protons identifies element similar to how your fingerprint ID’s you. Ex. 2 protons = He, 29 protons = Cu ALWAYS!!

How do we know the number of subatomic particles in an atom?
Mass number: number of protons and neutrons in nucleus (p+ + no) Ex: hydrogen can have a mass # of 3. Since it has 1 proton it must have 2 neutrons # of neutrons = mass # - atomic #

What are Isotopes? Atoms of same element with different # of neutrons
Same atomic # Different mass # (b/c neutrons are different) Ex. Carbon 12, Carbon 13, and Carbon 14 all naturally occurring isotopes of Carbon. Each has 6 p+ and 6 e-, but each has different # of neutrons (therefore, different mass#)

Determining the number of protons and neutrons
Li has mass # of 7 and atomic # of 3 Protons = 3 (same as atomic #) Neutrons= 7-3 = 4 (mass # - atomic #) Ne has a mass # of 20 and an atomic # of 10 Protons = 10 Neutrons = = 10

electrons are equal to protons So e- = p+ = atomic # Ex: He has mass # of 4 and atomic # of 2 p+ = 2 no = 2 e- = 2 Basic Atomic Structure 1:57

Determine the number of subatomic particles in the following:
Chlorine has a mass # of 35 and an atomic # of 17 p+ = 17, no = 18, e- = 17 Potassium has a mass # of 39 and an atomic # of 19 P+ = 19, no = 20 e- = 19

Candy Atoms Atom #1 - mass # of 5 and an atomic # of 3.
Atom #2 – 5 protons and 7 neutrons. Atom #3 – Atomic # of 7 and 8 neutrons.

Candy Atoms Atom #4 – mass # 18 and 9 electrons
Atom #5 – build your own candy atom using the candies that you have. You should be able to accurately determine: Atomic # Mass # # of protons, neutrons, and electrons

4.3 Modern Atomic Theory

Bohr Model of the Atom Agreed with Rutherford Devised planetary model
Small nucleus w/ lots of space Devised planetary model trying to show why e- were not sucked into p+ in nucleus of atom. e- in specific energy levels

Misconceptions from the Bohr Model
Bohr model good for diagramming atoms and energy levels e- do NOT move like planets in predictable orbits Mathematics determine probable location of e-

Energy Levels Possible energies e- can have Like floors in hotel
Floor nearest nucleus - ground floor

The Electron Hotel Levels nearer nucleus have lower energy (ground floor of hotel) Electrons fill energy levels from inside - outside. (ground floor - top floor of Electron Hotel)

Electron distribution in an Atom
Energy Level 3d 3 3p 3s ENERGY 2 2p 2s 1 1s NUCLEUS

Energy Levels Can’t stand “in between” steps in hotel stairwell
e-’s can’t exist “in between” energy levels Must absorb right amt of energy in order to move up energy levels Must lose right amt to move down

Evidence of Energy Levels
Energy gains & loses can be measured As e- drop orbitals, energy released in form of light/heat Like in fireworks (2:34)

Electron Cloud Model Electrons travel around nucleus in random orbits.
cannot predict location at any given moment. Electrons travel so fast, they appear to form a “cloud” around nucleus. Ex. - Airplane propeller

Atomic Orbitals Rooms in “Electron Hotel”
Region of space where e- likely located Each orbital can have 2 e- max Denser region = higher probability Energy Levels, Orbitals, and Electrons Energy Level (floors in hotel) Number of Orbitals (hotel rooms) Maximum number of electrons (occupants) 1 2 4 8 3 9 18 16 32

Electron Configuration
Arrangement of e-’s (occupants) in orbitals (rooms) Each orbitals holds 2 e-’s max (1 double bed) Stable when e-’s in orbitals w/ least energy Ground state i.e. Lithium (atomic # = 3) has 1st 2 e-’s in the 1st energy level (fills up 1 room w/ double bed) 3rd e- goes to 2nd energy level

Electron Configuration
If Lithium absorbs enough energy, 3rd e- jumps energy levels Excited state Less stable (like gymnast on beam) Eventually releases energy (often as light) Returns to ground state

How exactly are the particles arranged?
Bohr Model of the atom: Electrons move in orbits at fixed distances from the nucleus (planetary model) All of the protons and the neutrons The 3rd ring can hold up to 18 e- The 1st ring can hold up to 2 e- The 4th ring and any after can hold up to 32 e- The 2nd ring can hold up to 8 e-

What does carbon look like?
Mass # = 12 atomic # = 6 p+ = 6 no = 6 e- = 6 6 p and 6 n live in the nucleus

Drawing Atoms Draw the following atoms in your notes:
1. Beryllium has an atomic # of 4 and a mass # of 9

Beryllium Atom

Drawing Atoms 2. Sodium has an atomic # of 11 and a mass # of 23

Sodium Atom