Problems with bohr, quantum mechanics, electron configuration, periods, groups, trends UNIT TEST 2 CHEM
Problems with Bohr (shell) Concept
Bohrs Model successfully explained the line spectrum of hydrogen (1e)
As the number of electrons increased his model could not explain their line spectrum.
Sub energy levels were thought to exist.
Scientist in the 1920s suggested that the electron could not be visualized as a discrete particle moving in some type of orbit around the nucleus.
It was necessary to think in the terms of the chance of finding the electrons in certain spaces around the nucleus (orbitals)
What did Quantum Mechanics do? Successfully explains the line spectra of all elements.
The fundamental concept is unlike charges attract and like charges repel.
+1- attract -1-repel
Therefore, electrons will always be attracted towards the nucleus (positive attractive force) be repelled by each other causing them to be in different spaces around nucleus.
In order to minimize repulsions between electrons the distance between the orbitals growed/maximized.
Quantum mechanics describes the location and behavior of electrons in any atom BASED ON QUANTUM NUMBER.
The Principal Quantum Number "n"
Tells us how far the electrons are from the nucleus
It can be any whole number and replaces the shell notation
Electrons in first shell have a positive quantum number of 1 second has a pqn of 2
The Orbital Quantum Number
Describes the shape of the electrons orbitals
They exist b/c electrons repel each other and are attached to positive nucleus
They seek to minimize repulsions and maximize distance between them
4 types of orbital shapes
S orbitals spherical shape
P orbtials have infinity sign/dumbell shape
D orbitals have complex shapes
F orbitals have even more complex shapes
The magnetic quantum number
The orientation of the electron orbitals in the presence of a magnetic field.
In any energy level there can be 1s orbital, 3p orbitals, 5d orbitals, 7f orbitals
The spin quantum number
The electrons is a small negative particle spinning on its axis creating magnetic field
There are 2 spinning motions clockwise (magnetic field pointing NORTH) and counterclockwise (south)
Unlike magnetic fields attract to each other (+,-) can overcome negative repulsions and lead to electrons pairing off in orbitals
AN ORBITAL CAN CARRY 0,1 or 2 ELECTRONS
Electronic configuration of an element provides us with a description of the arrangement of the electrons in the atoms of that element
There are 2 principles in understanding how electrons are arranged 1.NUCLEUS IS POSITIVE SO ELECTRONS ATTRAC TO IT (lower energy shells are filled first) 2.ELECTRONS ARE NEGATIVE SO THEY REPEL EACH OTHER (limits # of electrons that can be in any region)
To summarize Electrons are attracted to nucleus. GREATER NUMBER OF PROTONS IN NUCLEUS GREATER THE POSITIVE ATTRACTIONS FOR ELECTRONS. Electrons repel each other within an energy level. Sideways repulsions from s,p,d and f orbitals. this determines number of electrons that can be in any shell.
PERIODIC LAW If elements are arranged in order of increasing atomic number a pattern can be seen in which similar properities occur
Groups The vertical columns on the periodic table (chemical families).
Groups include elements with similar properties
Groups have iupac/numbering system Groups 1-18
Groups had an old labelling system Roman numerals with letters a and b
Groups includes elements with simular properties
Elements in a group have same number of electrons in out most shell/orbit
Electrons in outermost shell are called valence electrons
Periods are the horizontal rows in the periodic table
Period numbering system 1,2,3,7 (from top to bottom of table)
Each period represents an electron shell or orbit
Metals, Non Metals, and Metalloids
Representative elements are the groups with roman numerals
Transition elements are the groups with roman numerals
Inner transition elements are the LANTHANIDES (ATOMIC NUMBER 57-70) and the ACTINIDES (ATOMIC NUMBER 89-102)
Chemical Groups (families)
Alkali Metals Group 1, soft, VERY REACTIVE stored under oil to prevent them from reacting with oxygen in air, oxides and hydroxides dissolve in water to give alkaline solutions, form with ions with single charge, react with some non metals to from white salts *(sodium chloride). have low melting points, low boiling points and low densities
Alkaline Earth Metals Group 2, react with water, not as reactive as group 1, found in nature
Halogens Group 17, poisonous with strong smell, froms molecules of 2 atoms, reacts with metals to form salts (NaCL, Li, L) Halogen ions have single negative charge
Noble Gases Group 18, low melting points , stable, full valence shell, exist as single atoms
Transition Metals centre blcok of PT, hard and dense, good conducters, form coloured ions and compounds, form alloys with other metals
Trends in the Periodic Table/Atomic Radius
Atomic Radius radius of atom, atoms volume
DECREASES WHEN YOU GO LEFT TO RIGHT BECAUSE Nucleus of atom GAINS PROTONS INCREASING POSITIVE CHARGE and attractive force between oppositive charges in nucleus become STRONGER
INCREASE WHEN YOU GO DOWN A GROUP energy level increases
Trends in Pt/Ionization Energy
AMOUNT OF ENERGY NEEDED TO REMOVE OUTER MOST ELECTRONS AGINST ATTRACTIVE FORCE OF NUCLEUS
INCREASES WHEN YOU GO RIGHT OT LEFT BECAUSE ELEMENTS ON RIGHT WANT TO TAKE OTHER ATOMS ELECTRONS TO BECOME STABLE
DECREASES WHEN YOU GO DOWN A GROUP B/c ELECTRONS ARE FURTHER FROM NUCLEUS MAKING IT EASIER TO REMOVE
Measured in Kj/mol
Requires more energy to lose than gain
Easy to remove ooutermost electrons from those atoms that have many electrons (elements near bottom of the pt)
Trends in Pt/Electronegativity
This is the atoms desire to grab another atoms electrons (give away theirs)
INCREASES AS YOU MOVE LEFT TO RIGHT BC IT IS EASIER TO GIVE AWAY THAN TAKE THEM
DECREASES AS YOU GO DOWN A GROUP (atomic number increases)
Trends in the Pt/ Electron Affinity
MEASURES THE CHANGE IN ENERGY THAT OCCURS WHEN AN ELECTRON IS ADDED TO THE OUTER ENERGY LEVEL OF AN ATOM TO FORM NEGATIVE ION
INCREASES AS YOU MOVE LEFT TO RIGHT
DECREASES AS YOU GO DOWN A GROUP FIRST ELECTRON AFFINITIES BECOME LESS
HIGH NEGATIVE NUMBERS MEAN A HIGH ELECTRON AFFINITY LOW NEGATIVE NUMBERS MEAN A LOW ELECTRON AFFINITY
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