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Fundamentals of Chemistry (Electrons (How many electrons per shell (1st…
Fundamentals of Chemistry
What is an Atom
The smallest unit of an element
Consists of a central nucleus surrounded by one or more electrons
What is the Nucleus
The central part of an atom
Composed of protons and neutrons
What is a Proton
Positively charged particle
Found within an atomic nucleus
What is a Neutron
Uncharged particle
Found within an atomic nucleus
What is an Electron
Orbit the nucleus in layers called shells
With a charge of negative electricity
Mass is 1800 times smaller than proton + neutron
Mass of a proton is the same as a neutron
The forces that holds the nucleus together is called the nuclear force
All matter is composed of atoms
Periodic Table
Columns are called groups, rows are periods
Atomic mass = mass of the element. # Of protons and neutrons
Atomic number =number of protons
An element can have a different number of electrons or neutrons
Isotopes
Atoms of the same element having different masses
Same number of protons, different number of neutrons
Molecular Weight
The weight of the molecule, the molecular weight, is the total mass of the individual atoms
Electrons
Are moving within specific volumes of space - orbital
Electrons can occupy several different types of orbital
Orbital have different shapes
Located at varying distances from the nucleus
Orbitals are grouped into families we call shells, which are identified by a number 1,2,3,4,5,6,7 (energy level)
How many electrons per shell
1st shell contains one S orbital
2 electrons
2nd shell contains one s orbital and three p orbitals
8 electrons
3rd shell contains one s orbital, three p orbitals and five d orbitals
18 electrons
Subshell shapes S and P orbitals
s,p,d and f different shapes
Periodic trends
Metals: conduct heat, electricity and very shiny are malleable
Non metals: poor conductors of heat, electricity and when solid are brittle
Metalloids: characteristics of metals and non metals, which vary with the element
Octect rule: Atoms will be more stable if they have a filled s and p orbitals for their outermost electrons (called valence electrons). Many elements will either lose or gain electrons from other atoms in order to achieve this full octet.
Electronegativity: Ability of an atom to attract electrons towards itself in a chemical bond
Increase Electronegativity across the table
Down the group electronegativities decrease in halogens
When two atoms of equal electronegativity bond - the are equally electronegative, Same tendency to attract the bondy pair of electrons, Electrons average half way between the two atoms, NON POLAR BOND is formed
When atoms bond with different electronegativity values this results in unequal sharing of electrons.
Polarity of Molecules- Non polar
Occurs when polar bonds cancel each other
Types of Bonding
Ionic Bond: Occurs between a metal and a non metal
Electrons are transferred from the metal to the non-metal atom
Covalent bond occurs between two non metal atoms
sharing of electrons. Strong force that joins them together.
Shared electron pair = bonding pair
Triple bond = three pairs of shared electrons
Metallic bond occurs between atoms in a metal
Delocalized bonding resonance: one pair of bonding electrons is spread over the region of all three atoms
Resonance description is to draw all the possible electron dot formulas.
Coordinate covalent bond or dative bond: one atom provides both electrons of the shared pair.
Formation of ions
Atoms completely full outer electron shells by either gaining or losing electrons: Atoms become Ions
Unlike atoms: Ions have an electrical charge + Contain an unequal number of protons and electrons
Ionic Bonding
Metal tend to lose electrons and become positive cations (positive charge)
Non metals gain electrons and become Negative anions (Negative charge)
Formal Charge = difference between the number of valence electrons in the free atom and the number of electrons assigned to that atom in a lewis structure.
Formal charge = (n of electrons in valence shell of the free atom) - (n of bonds to the atom)- n of unshared electrons
Most plausible structure is the one with no formal charges
VSEPR Theory: Electrons are negatively charged, they should be most stable when they are separated as much as possible
Shapes
Linear 180
Trigonal Planar 120
Tetrahedral 109.5
Lone pair electrons spread out more than bond pair electrons
Trigonal Pyramidal 107
Bent shape 104.5