atoms and the periodic table chapter 4 meet the elements
TRANSCRIPT
ATOMS AND THE PERIODIC TABLE
CHAPTER 4
Meet the Elements
VOCABULARY --- REVIEW and INTRODUCTION
Atoms – smallest part of an element that still retains all properties of that element.– Atoms can be broken down into subatomic
particles.– Atoms can combine to form molecules.
Molecule – the smallest part of a compound that still retains all properties of that compound.
ELEMENTS, ATOMS, MOLECULES, COMPOUNDS
Subatomic Particles
Nucleus – center of atom– Neutrons – no charge– Protons – positive charge
Energy Levels – located around nucleus– Electrons – negative charge
Electrons move in a cloud around the nucleus
Atomic Models
Bohr’s Model (1913)– Niels Bohr suggested electrons moved in orbits
around the nucleus … similar to planets moving around the sun.
– Each electron could only move in specific orbits or paths.
Atomic Models 1925 – Electron Cloud Model
– Electrons move in a region or general area surrounding the nucleus. (called an electron cloud)
– An electrons exact speed, direction or location cannot be determined at any one particular moment.
– Electrons are located at various distances around the nucleus
Electrons close to the nucleus have LOW energy Electrons far away from the nucleus have HIGH energy
Electron Cloud Model
Electrons exist in energy levels The number of energy levels that are filled will
depend on the number of electrons of that atom.
1st energy level holds 2 electrons 2nd energy level – 8 electrons 3rd energy level – 18 electrons 4th energy level – 32 electrons
Electron Cloud Model Octet Rule – An atom is considered stable
(happy) when its outer energy level is full of electrons. (8 outer electrons is considered stable).
Valence Electrons – Electrons found in the outermost shell of an atom – Valence Electrons determine the chemical properties of
an atom.– When valence shell is not full…the atom will be more
reactive
Dot Diagrams (Lewis Structure) and
Valence Electrons
Uses the symbol of the element and dots to represent the electron in the outer energy level
Periodic TableElement Song
Dmitri Mendeleev: Father of the Periodic Table
HOW HIS WORKED… Put elements in rows by
increasing atomic weight.
Put elements in columns by the way they reacted.
SOME PROBLEMS… He left blank spaces for
what he said were undiscovered elements. (Turned out he was right!)
He broke the pattern of increasing atomic weight to keep similar reacting elements together.
The Current Periodic Table
Mendeleev wasn’t too far off. Now the elements are put in rows by
increasing ATOMIC NUMBER!!
Periodic Table
The arrangement of elements according to repeating changes in properties
Each box on the periodic chart contain the atomic number, chemical symbol, name, and average atomic mass.
Periodic Table Organization
Groups – A vertical Column of elements– Elements in the same group have
the same number of valence electrons.
– Elements of the same group have similar chemical properties.
Periods – Horizontal Rows– The number of protons increase
by one from left to right (so do # of electrons)
Periodic Table Organization
Chemical Symbol – Abbreviated way to write the name of the element (EX: O – Oxygen)
Atomic Number – The number of protons in the nucleus
Atomic Mass Number – The number of protons plus neutrons in the nucleus (often a decimal number)– This number may be rounded…round up if it is .5 or
above and down if .4 or below)– The mass number is an AVERAGE
Ions and Isotopes
Ions – An atom or group of atoms that has lost or gained one or more electrons and has a negative or positive charge– Occurs when an atom gives up an electron or takes
an electron because outer energy levels are not full– CATION – positive ion (loses electrons and
becomes positive)– ANION – negative ion (gains electrons and
becomes negative)– (pictures)
Ions and Isotopes
Isotopes – An atom that has the same number of protons as other atoms of the same element do but has a different number of neutrons.– Isotopes are often radioactive
Used for cancer treatments, preserving foods, etc.
– Example: Hydrogen has three isotopes Protium, Deuterium, Tritium
Isotopes ofHydrogen and Carbon
Families of Elements
Members of a family in the periodic table have many chemical and physical properties in common…they have similar valence electrons.
3 Groups:– Metals, Nonmetals, Semiconductors
– The Periodic Table of Videos - University of Nottingham
Hydrogen
Hydrogen belongs to a family of its own.
Hydrogen is a diatomic, reactive gas.
Hydrogen was involved in the explosion of the Hindenberg.
Hydrogen is promising as an alternative fuel source for automobiles
Metals
Four different kinds of metals
Share common properties of: existing as solids at room temperature, shiny, good conductors of heat and electricity
1. Alkali Metals
Group 1 Very Reactive…Have only 1 valence electron Always combined with something else in
nature.– Example: Sodium must be stored in oil so as not to
react with moisture in air.
2. Alkaline-Earth Metals
Located in Group 2 Have 2 valence electrons Less reactive than Alkali Metals Always combined with nonmetals in nature Ex: Calcium and Magnesium
3. Transitional Metals
Groups 3-12 Much less reactive These elements properties gradually change
from being more similar to Group 2 to being more similar to Group 13 as you move from left to right
Examples: Gold, Platinum, Silver
4. Synthetic Elements
All elements above #92 are man-made Many are radioactive
Nonmetals
Located on the right side of the periodic table Includes some elements in Groups 13-16 and
all elements in Groups 17-18 Plentiful on Earth 3 Groups
1. Halogens
Group 17 Very Reactive Always combined with another element in
nature Has 7 valence electrons Used as disinfectants and to strengthen teeth
2. Noble Gases
Group 18 Unreactive; Do not
make compounds with anything.
8 Valence Electrons (full outer energy level)
3. Semiconductors (Metalloids)
Intermediate conductors of heat and electricity Includes 6 elements Located on the “stairstep line”
– Includes: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium
Diatomic Molecules
If these elements are found alone in nature they are always bonded to themselves because they are very reactive.– Example: O2, H2, Fl2, Br2, I2, N2, Cl2
There are 7– Including: Hydrogen, Oxygen, Fluorine, Bromine,
Iodine, Nitrogen, Chlorine