Objective 4 Element Compound Mixture
Elements, Compounds & Mixtures
Classify samples from everyday life as being element, compound or mixtures 10th
grade only
Periodic Table
Relate the chemical behavior of an element including bonding to its placement on the
periodic table
•Matter is anything that takes up space and has mass. All matter can be identified by its
characteristics.
•
Element. Composed of one kind of atom
ƒ •
Examples
1. •
Gold, Au
copper, Cu
2. •
•Compounds are two or more elements chemically combined together. This means that in order
to separate the elements from the compound requires chemical reactions. All compounds will
have a definite chemical formula (a formula that is always the same ratio of elements).
•
Examples:
1. •
Table salt, NaCl
Water, H2O
2. •
•Mixtures are two or more substances (a substance is any type of matter) that is combined, but
not chemical bonded together. Can be separated by simply means (tweezers, magnets,
evaporation).
•
Examples
concrete
1. •
2. •
bag full of garbage
•Mixtures can be of two types, heterogeneous and homogeneous.
ƒ •Heterogeneous means that it has different consistence throughout the mixture.
•
Examples
garbage bag of trash
1. •
2. •
chocolate chip cookie
ƒ •Homogeneous mixtures are the same consistence throughout.
•
Examples
1. •
Kool-aid
2. •
milk
ƒ •Solutions are another name for homogeneous mixtures.
ƒ •
Solutions have two parts:
ƒ •
solute = what is dissolved
ƒ •
solvent = what does the dissolving
ƒ •
Nine types of solutions. Solute can be liquid, solid or gas; solvent can be solid,
liquid, or gas. If the solvent is water, the solution is called an aqueous solution.
•
Examples
1. •
oxygen dissolved in nitrogen (AIR) solute = gas, solvent = gas
2. •
Dr. Pepper solute = carbon dioxide (gas), solvent = water (liquid)
3. •
Acetic acid in water (vinegar) solute = liquid, solvent = liquid
To help you decide if a homogeneous substance is a solution or a compound, ask yourself this
questions: "Are there more than one type of this substance?" If you answer yes, then it is a
solution (mixture), if no, then it is more likely a compound.
To help you decide if a mixture is homogeneous or heterogeneous, ask yourself "is it the same
through out?" if yes = homogeneous, no = heterogeneous.
The following flowchart will help.
.
Comparing Solutions, Colloids, and Suspensions
Description
Solutions
Colloids
Suspensions
Homogenous
Heterogeneous
Heterogeneous
mixture
mixture
mixture
Settle while
NO
NO
YES
standing
Can be separated NO
NO
YES
using filter paper
Sizes of particles 0.1 - 1 nm
1 - 100 nm
Greater than 100
nm
Scatter light
NO
YES
YES
The Atom (Simple Bohr Model)
Atom is the smallest part of an element that retains all the properties of that element.
Atoms are made up of even smaller particles--a nucleus consisting of protons and
neutrons and electrons in shells around the nucleus. The most common way to picture an
atom is the solar system model. The number of protons in the nucleus determines the
element, as well determining the number of electrons.
Solar system model
The solar system model of the atom is that the atom is like a tiny solar system, with the
nucleus in the center and electrons rotating around the nucleus in orbits, similar to how
the planets rotate around the Sun. It is also called the Bohr model, after Neils Bohr, who
discovered electron shells in 1913.
Electrons rotating around the neon nucleus
There are some newer models of how the electrons appear in the atom.
Nucleus
The nucleus consists of a number of positively charged protons and uncharged neutrons.
They are approximately the same size and weight.
Since like charges repel, there is some sort of "nuclear glue" that holds the nucleus
together. There must usually be more neutrons than protons for a nucleus to be stable, so
it has been thought that neutrons had something to do with this nuclear glue. Present
theories state that there is a sub-nuclear particle called a gluon that holds the nucleus
together. The atomic number of an element is the number of protons in the nucleus of an
atom of that element.
Electrons
Atoms are neutral and therefore have the same number of negatively charged electrons in
orbit around the nucleus as there are positively charged protons in the nucleus. In
situations where there are either more or less electrons in orbit than there are protons in
the nucleus, the atom is called an ion.
Electron Energy Levels
Electrons are arranged in energy levels (shells) or orbits around the nucleus.
Maximum number
There is a definite arrangement of the electrons in these shells and a maximum number of
electrons possible in each shell.
12 3 4 5
Shell or Orbit Number
Maximum Number of Electrons 2 8 18 32 50
The maximum number of electrons in the first energy level is 2. After the energy level is
filled, the second starts filling up, according to the number of positive charges in the
nucleus. The maximum number of electron in the second energy level is 8 electrons.
Then the third shell starts to fill.
Electron shells for a Sodium atom
(atomic number 11, with 11
electrons)
Filling order complicated. After the second orbit or shell is filled, things start to get
complicated. The third shell fills until it gets to 8, and then the fourth shell starts adding
electrons until it too has 8 electrons. Then the third shell fills until it gets to 18.
Outer shell basis of Chemistry (For TAKS Only)
Periodic Table
LElements listed by atomic number= number of protons = number electrons
LThe elements are listed by their abbreviations. H = Hydrogen, He = Helium, and so
on.
LThey also usually include the atomic weight of each element in the Periodic Table
LThe number of each Period or row (1, 2, 3, 4,...) also indicates how many orbits all the
elements in that row have. Thus every element in row 2 has two orbits or electron energy
levels or shells.
LGroups are vertical columns and are now numbered 1-18. All elements in the same
group have the same number of valence electrons (electrons in the outer energy level) and
react similarly. Now, you know that there are a maximum number of electrons allowed
in each orbit. Only 2 can be in the first orbit, 8 in the second, 18 in the third, 32 in the
fourth, and so on.
Outer
Orbit
+1
+2
+3
4
-3
-2
-1
Full
Orbits
1
1H
2
3 Li
4 Be
5B
3
11 Na
12 Mg
13 Al 14 Si 15 P 16 S 17 Cl
4
19 K
20 Ca *
*
*
*
33 Br 34 Kr
The Periodic Table (partial version)
2 He
6C
7N
8O
9F
10 Ne
18 Ar
LChemical reactions -The Periodic Table helps to predict chemical reactions.
Completing orbitsÆ Elements will lose or gain electrons to have eight electrons (same as
noble gas) in their outer energy level.
As you know, atoms "like" to have their outer orbit completely filled or completely
empty. (Only for TAKS) Thus Hydrogen has 1 more electron than having its orbit empty.
Since Boron (B) already has its first orbit full and will allow a maximum of 8 electrons in
its second orbit, +3 indicates it has 3 more electrons than having its outer orbit empty.
Likewise, Chlorine (Cl) is one electron short (-1) of filling up its outer orbit or energy
level.
Groups are or vertical columns and are now numbered 1-18. All elements in the same
group have the same number of valence electrons (electrons in the outer energy level) and
react similarly. Elements will lose or gain electrons to have eight electrons (same as
noble gas) in their outer energy level.
GROUP
1 (IA)
VALENCE
ELECTRONS
1
2 (IIA)
2
13 (IIIA)
3
14 (IVA)
4
15 (VA)
5
16 (VIA)
6
FAMILY NAME
REACT
Alkali metal
Lose 1 electron &
be become an ion
with a +1 charge.
Lose 2 electron &
be become an ion
with a +2 charge
MetalÆLose 3
electron & be
become an ion with
a +3 charge
NonmetalÆ gain 4
electrons and form
ion with a -4 charge.
NonmetalÆ gain 3
electrons and form
ion with a -3 charge
NonmetalÆ gain 2
electrons and form
ion with a -2 charge
Alkaline metal
17 (VIIA)
7
Halogens
18 (VIIIA)
8
Nobel Gases
NonmetalÆ gain 1
electrons and form
ion with a -1 charge
Non-reactive
LArrangement of elements
The elements in the following Periodic Table are arranged in rows (Periods) according to
atomic number and in columns (Groups) according to the configuration of the outer orbit
(energy level).
Periods Ærows and GroupÆcolumns
ƒ If you go along a period from left to right, the elements are
numbered 1 - H, 2 - He, 3 - Li, 4 - Be, 5 - B, and so on. The atomic
number is also the number of protons in the element's nucleus.
ƒ If you go down a group, each element has the same number of
electrons in its outer orbit or shell. For example, H, Li, Na, K and
so on, all have one electron in the outer energy level. On the other
hand, O, S, Se, etc. all have 6 electrons in the outer orbit. The
number of electrons in the outer energy level determines the
element's chemical properties.
LProperties
Metals, nonmetals and Metalloids (semimetals)
ƒ Elements B, Si, Ge, As, Sb, Te, and At are metalloids. They conduct heat and
electricity better than nonmetals, but not as well as metals. They are easier to
shape than nonmetals, but not as easy as metals. All are solid at room
temperature.
ƒ Elements on the right of the periodic table are Nonmetals. They are poor
conductors of heat and electricity and not easily formed into shapes. Most are
gases at room temperature, except for C, P, S, Se and I, which are solids and Br,
which is a liquid. H is also a nonmetal.
ƒ Elements on the left side of the periodic table are metals. They are solid
substances that are a good conductors of heat and electricity. They can be formed
into many shapes.
g
What is Chemical Bonding?
Chemical Bonding - the combining of atoms of elements to form new substances
(compounds)
Atoms contain a positively charged center or nucleus. Outside the nucleus are negatively
charged electrons. The atom as a whole is neutral - the positive charge balances the
negative charge.
The positively charged nucleus attracts the negative electrons. This holds the atom
together.
Electrons are not pulled into the nucleus. They remain in a region called the electron
cloud.
The electron cloud is made up of energy levels. The 1st level can hold 2 electrons. The
2nd can hold 8 electrons. The 3rd can hold 8 electrons if the 3rd level is the outermost
level (the valance electrons) or up to 18 if it is not the outermost.
Valance electrons - the electrons in the outermost energy level. The maximum number is
8. These are the electrons involved in chemical bonding.
If the outer energy level is filled with 8 electrons, the atom is stable and does not react
(such as the Noble gases - Family VIIIA)
To achieve stability (which means a filled outer energy level), an atom will either gain or
lose electrons. Atoms that gain electrons will bond with other atoms that lose electrons if
the bonding gives both atoms a complete outer energy level with 8 electrons.
Ionic Bonding –
Between a metal and a nonmetal atom
bonding that involves a transfer of electrons. It involves a formation of ions or "charged"
atoms. One atom gains electrons and the other atom loses electrons.
An atom that gains electrons has a negative charge. It is a negative ion. Example: A
neutral fluorine atom gains one electron to form a fluoride ion (F-1)with a -1 charge.
An atom that loses electrons has a positive charge. It is a positive ion. Example: a neutral
sodium atom loses 1 electron to become a sodium ion (Na+1) with a positive 1 charge.
Positive ions attract negative ions and form ionic bonds.
For example, during the reaction of sodium with chlorine:
sodium (on the left) loses its one valence electron to chlorine (on the right),
resulting ina positively charged sodium ion (left) and a negatively charged chlorine ion
(right).
Covalent Bonds Between Nonmetal Atoms
Covalent bonds are forces of attraction formed when atoms of a molecule share electrons.
The term sharing electrons indicates that the valance electrons of the atoms become part
of the orbitals of more than one atom of the molecule.This is illustrated in the following
diagrams
In the figure below are shown two individual hydrogen atoms. Each atom has one
valance electron and a nucleus with one proton.
In the figure below two hydrogen atoms share the electrons of the valance orbital of the
individual hydrogen atoms so that each hydrogen atom is now sharing two electrons. In
this figure are also shown two other ways of depicting the hydrogen molecule. The
depiction on the left is a capital H with a subscript 2 indicating there are two hydrogen
atoms make up this hydrogen molecule. In the depiction on the right are two H's
connected by a line. This line represents the single covalent bond composed of two
shared electrons.
Example water
Metallic Bonds –
Only Metal Atoms
bonds formed by the atoms of metals, in which the outer electrons of the atoms form a common
electron cloud or "sea" of electrons.
The positive nuclei of metal atoms are surrounded by free-moving or mobile electrons that are
attracted by the nuclei Only Metal Atoms