Science Lesson 3.3-3.4
a metal is made up of
positive metal ions with enough valence electrons "swimming" around to hold the ions together
covalent bond
this is the type of bond where electrons are shared between atoms Ex: H2O— electrons are shared between H's and O
nonmetals bond with nonmetals
covalent bond
water molecule
covalent bond
the four valence electrons of a carbon atom are in its
outermost energy level
in metallic bonding, there is a
"sea" or "cloud" of electrons
Bohr Model
shows the electrons but is not completely accurate (does not show the true arrangement of the electrons)
an atom of sulfur has
six valence electrons
valence electron
the electrons found in the outermost shell of an atom; this is where the chemical reactions and bonding takes place
the limited number of letters in the alphabet can be used to make many words, so
the elements combine to make many compounds
chemical changes change
the identity of substances
valence shell
the outermost shell of an atom
oxidation number
the total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom
atoms are not created or destroyed by the chemical change
there were the same number and types of atoms before and after the chemical change
metalloids
these touch the staircase in the periodic table and have properties of both metals and nonmetals
best choice to show how atoms are arranged in molecules
Space Filling Model
when chlorine joins with sodium
chlorine gains one electron from sodium and becomes 1-
there are a few atoms in water
compared to the large amount of atoms in DNA
covalent compounds
compounds formed when covalent bonds occur
ionic compound
compounds formed when ionic bonds occur
Space-Filling Model
does not show characteristics of the atoms but shows their connections
if atom loses at least one electron
it will now have fewer electrons than protons; this results in overall positive charge
metallic bond forms between
metal atoms when their outermost energy levels overlap
metals bond with metals
metallic bond
80% of elements
are metals
covalent bond forms when
two nonmetal atoms atoms share one or more pairs of electrons
ionic bond
type of bond where atoms give electrons to other atoms and there is an attraction between oppositely-charged ions
an atom tends to form bonds
when its outermost energy level is not full
atoms are reactive
when their outermost energy levels are not full
when atoms are rearranged
chemical bonds have to be formed or broken
hydrogen
1 valence electron
sodium
1 valence electron
steps with metallic bonds to turn on a lamp
1. When you turn on a lamp, electrons move through the copper wire that connects the light bulb in the lamp to the electrical outlet. 2. The electrons that move are the valence electrons in the copper atoms. These electrons are free to move because the electrons are not connected to any one atom.
helium
2 valence electrons
carbon
4 valence electrons
chlorine
7 valence electrons
neon
8 valence electrons
H2+Cl2
=2HCl
chlorine atom fills its outermost energy level
Chlorine atom has seven valence electrons. It needs one more electron to have a full outermost energy level. Chlorine atom can gain an electron from a sodium atom. When this happens, chlorine atom becomes a negative ion (anion). The sodium atom that loses the electron becomes a positive ion (cation). The ions formed by both sodium and chlorine have eight valence electrons. Their outermost energy levels are now full. The negative and positive ions are held together by bonds. The result is sodium chloride (table salt).
using the periodic table to find valence electrons
Each family (column) of elements (excluding families 3-12) has a set number of valence electrons to its atoms. The first family has one valence electron. The second family has two, the thirteenth family has three, the fourteenth family has four, and so on.
not all of an atom's electrons
can interact with the electrons of other atoms to form bonds
fall leaves
The color of fall leaves is the result of a chemical change. Green pigments (chlorophyll) break down, but red and yellow pigments don't break down as easily. The green pigment's atoms are rearranged to become clear.
Bohr Model and valence electrons
The valence electrons are the electrons on the outer ost "layer" of the atom. The Bohr Model shows the number of valence electrons of each atom.
lithium, sodium, and potassium atoms are almost never found alone in nature
They are very reactive and form chemical bonds with other atoms. They are reactive because they only have one valence electron.
ion
a charged particle that forms when an atom loses or gains an electron
molecule
a group of atoms that are held together by chemical bonds
when two nonmetal atoms bond
a large amount of energy is needed for either atom to lose an ELECTRON, so, instead, they share so both will have filled outermost energy level
ion
a particle with a positive or negative charge
ion forms when
an atom gains or loses electrons from its outer, or valence, shell
chemical bond
an interaction that holds atoms or ions together
octet rule
atoms tend to gain, lose, or share electrons so as to have eight valence electrons
anion
atoms that gain electrons and have a negative charge
cation
atoms that lose electrons and have a positive charge "paws"
a chemical bond joins
atoms together in a water molecule
ionic bond forms when
atoms transfer one or more electrons to another to form a bond (brings oppositely charged ions together)
octet rule
atoms want to have 8 electrons in their outer shell to be stable
ions
atoms with either a positive or negative electrical charge
bonds are important for atoms
because forming bonds allows atoms to fill their outermost energy level (valence shell)
metals can be shaped
because of the nature of the bonds that form between metal atoms
during a chemical change
bonds break, and new bonds form
an atom can form bonds with other atoms
by gaining, losing, or sharing electrons
these atoms form bonds
by gaining, losing, or sharing valence electrons to form bonds
H2O bond
covalent bond in which two hydrogen atoms share their electrons with one oxygen atom; oxygen keeps most of the electrons, so it is negative; the hydrogens don't have many electrons, so they are positive
physical properties of ionic compounds
crystal lattice structure (think salt); crystals are hard and brittle— will break before they bend (hammer); poor conductors of electric current due to ions held tightly in place (if it melts, it becomes a better conductor); soluble in water (dissolves)
number of protons
does not change
the nucleus of an atom
does not change when an atom undergoes a chemical reaction
atoms are rearranged
during a chemical change when bonds break and form
best choice to show the locations of the parts of a sodium atom
electron cloud model; it shows the region where the electrons are found and the locations of the other parts of the atom
nitrogen atoms have
five valence electrons
ductile, ductility, etc.
formed into thin wires
(ionic bond) electrons are tranferred
from a metal (+) to a nonmetal (-)
(ionic bond) valence electrons move
from outer shell of the metal atom to the outer shell of the nonmetal atom
oxygen would like to
gain 2 electrons
nitrogen would like to
gain 3 electrons
carbon would like to
gain 4 electrons
properties of metallic bonds
good electrical conductors due to electrons moving freely; malleable and ductile due to free-moving electrons
malleable
hammered into sheets
metallic bonds
have metal ions and free electrons from outer shells of metal atoms
first electron shell can
hold 2 electrons
outermost electron shell can
hold 8 electrons
Which atoms are likely to form chemical bonds with other atoms?
hydrogen, sodium—> lose their one valence electron chlorine—>has 7 valence electron, wants to gain one carbon—> gain or lose 4 valence electrons They all don't have a full valence shell
atoms will be neutral
if there is an equal number of electrons and protons
nonmetals bond with metals
ionic bond
sodium chloride molecule
ionic bond
if atom gains at least one electron
it will now have more electrons that protons; this results in overall negative charge
nitrogen atoms are
likely to form bonds with other atoms because they do not have full valence shells
physical properties of covalent compounds
low solubility in water (some do, some don't) Ex: wax doesn't dissolve in water; low melting and boiling points— covalent bonds don't break as easily as ionic bonds do; poor electrical conductivity— most are unable to conduct electricity
copper metal is held together by
metallic bonding, in which electrons flow around copper ions
metallic bonds are
responsible for the properties of metals
Electron Cloud Model
shows the locations of the parts of the atom but does not show individual electrons
when sodium joins with chlorine
sodium loses one electron to chlorine and becomes 1+
chemical changes don't change
the number of atoms (don't create or destroy atoms)
how many of each type of atoms are there before and after a chemical change
the same amount
metals
these are found to the left of the staircase and form ionic bonds with nonmetals: give away electron(s) and become positive (hydrogen is the exception)
nonmetals
these are found to the right of the staircase and form covalent bonds with each other, or take electrons away from metals to form ionic bonds and become negative
hydrogen and oxygen of H2O are bonded
where each hydrogen touches the oxygen
The Bohr model of a neon atom (versus that of a nitrogen atom)
would have 10 electrons and 8 valence electrons instead of 7 electrons and 5 valence electrons