Transcript atoms II - Doral Academy Preparatory

Atoms
Atoms smallest particle that an element
can be divided into.
 Atoms comes from the Greek word
atomos which means “invincible.”
 Atoms are made up of even smaller
particles called protons, neutrons, &
electrons.
 Protons & neutrons stick together to form
the nucleus, which is the center of the
atom.
 Electrons are located surrounding the
nucleus in the electron cloud.

Dalton's Atomic Theory (1803)
•All matter is composed of extremely small
particles called atoms.
•Atoms are the building blocks of matter.
•All atoms of a given element are identical in
size, mass, and other properties. Atoms of
different elements differ in size, mass, and other
properties.
•Atoms cannot be subdivided, created, or
destroyed.
•Atoms of different elements can combine in
simple, whole-number ratios to form compounds.
•In chemical reactions, atoms are combined,
separated, or rearranged.
Modern Atomic Theory
1.Elements are composed of atoms, which
are extremely small.
2.All atoms of a given element have the
same chemical properties and contain the
same number of protons.
3.Compounds are formed by the chemical
combination of two or more different kinds
of atoms. (Whole numbers only)
4.Atoms are the units of chemical change.
Atoms are composed of three types
of particles
Particles
Symbol
Charge
Location
Protons
p+
Positive
charge
Found in the
nucleus
Neutrons
N0
Neutral (no)
charge
Found in the
nucleus
Electrons
e-
Negative
charge
Found orbiting
the nucleus
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John Dalton proposed that all substances are made
up of atoms.
These atoms are small dense spheres that cannot be
created or destroyed.
J.J Thompson proposed that atoms were made up of
small particles called protons (+) & electrons (-).
However J.J did not know where the p+ or e- where
located. He thought they we are evenly distribute
Earnest Rutherford proposed that an atom had a
dense positively charged nucleus surrounded by
electrons (-)
Niels Bohr 2 years after Rutherford proposed his
theory Bohr stated that electrons revolved around
the nucleus in circular paths called ORBITS.
Bohr also stated that there could only be a certain
amount of electrons in each orbit.
Brief history of atomic Theory development
Year
Milestone
Scientist(s)
The first coherent atomic theory
Democritus
1804
First "modern" atomic theory
J. Dalton
1869
First periodic table
D. Mendeleev
Radioactivity discovered and identified
H. Becquerel, M. Curie,
E. Rutherford
Electron discovered
J.J. Thomson
Identification of an atomic nucleus
E. Rutherford, H. Geiger
1913
Mass of electron determined
R. A. Millikan
1913
Positive charge in the nucleus and naturally
occuring isotopes discovered
J.J. Thomson
1913
Atomic number determined, periodic table
reorganized
H. Moseley
1919
Proton existance confirmed, neutron
proposed
E. Rutherford
1931
Neutron Identified
J. Chadwick
~400 BC
1896-9
1897
1909-11
All matter is made of different kinds of
atoms.
 Different atoms are called ELEMENTS.
 Two or more elements can combine to
form COMPOUNDS.
 Elements are considered the simplest form
of matter.
 Elements CAN NOT be broken down.
 There are 110 elements in the universe.
 92 are found naturally on earth / in its
atmosphere.
 18 are made in laboratories.

 Each
element is made of the SAME type
of atom.
 Example: the element Oxygen is made
out of oxygen atoms.
 Example: the element hydrogen is made
out of hydrogen atoms.
•Earth’s crust is made up mostly of the
elements oxygen & silicon
•Earth’s atmosphere is about 78% nitrogen &
21% oxygen
Protons + neutrons
# of protons
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•Every atom is made up of a nucleus (which
contains protons and neutrons).
•The nucleus is the center, and it contains most of
the mass of the atom.
•Outside the nucleus there are electrons, which are
extremely small, and which move around the
nucleus very quickly.
•The electrons are segregated into "shells" which
are like invisible spheres that go around the atoms.
•Only two electrons can be in the innermost shell.
The next track will take eight atoms.
Calculating the # of electrons in
each shell
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In other words, electron shells have a limited
capacity for electrons.
As you might expect, the farther an electron
shell is from the nucleus, the larger it is.
You can calculate the total capacity of an electron
shell using the formula 2n2, where n equals the
number of the electron shell.
For example, for the 1st electron shell n = 1 and
2 x 1x1 = 2, telling us that the capacity of the
1st shell is 2 electrons as we have already seen.
For the 2nd shell (n = 2) and 2 x 2x2 = 8. For
an atom to fill its 2nd electron shell, it would
need 10 electrons: 2 to fill the 1st shell and 8 to
fill the 2nd.
The 3rd shell has a total capacity of 2 x 3x3 =
18 electrons.
Shell
Number
2 * (the shell number * the
shell number)
= the maximum number of
electrons in this shell.
Maximum Number
of Electrons in the
Shell
1
2 x (1 x 1) = 2
2x1=2
2
2 x (2 x 2) = 8
2x4=8
3
2 x ( 3 x 3) = 18
2 x 9 = 18
4
2 x (4 x 4) = 32
2 x 16 = 32
5
2 x (5 x 5) = 50
2 x 25 = 50
There are five possible shells
available to atoms. This diagram
shows only three shells, and some
atoms, such as the little hydrogen
atom, use only the one inner shell.
Each of the elements has a
different number of the tiny
electrons, and a corresponding
number of protons. Hydrogen is the
smallest, with only one electron.
Carbon, nitrogen, and oxygen, are
also small, light atoms.
Valence electrons
 The
electrons found on the
outermost energy shell of an atom.
 The outer shell electrons that are
available for and capable of forming
bonds with other atoms. Valence
electrons are electrons occupying the
outermost energy level.
Electron configuration shorthand
Hydrogen
Lithium
Fluorine
Sodium
H )1eLi )2e- )1eF )2e- )7eNa )2e- )8e- )1e-
This is a diagram of an atom of neon gas. I have colored the
nucleus orange and the electrons blue. The inner shell is filled
by two electrons. The next shell is filled too -- with eight
electrons. Neon doesn't need any more electrons to fill its
outermost shell, so it doesn't participate in chemical reactions.
It is what we call an inert gas, one that doesn't combine with
other elements.
Now we see a very different situation. Here we have a carbon atom
near two hydrogen atoms. Note that the carbon atom has two
electrons in the inner ring: that is filled. But in the next ring, it has
four empty spaces! The hydrogen atoms, too, could each use another
electron.
Now lets look at some more atoms. Here we see that four hydrogen atoms
are sharing their electrons with the carbon atom! They have filled the
empty ring spaces in the carbon atom, and the carbon atom is sharing its
electrons as well. We now have a molecule of methane gas! This is real
chemistry!
The materials that the earth are made of can be
thought of as being of two kinds: elements and
compounds.
Elements, such as oxygen (O), gold (Au), iron (Fe),
nitrogen (N), and carbon (C), cannot be broken down
into anything else.
Compounds, such as carbon dioxide, salt, and water,
are made of combinations of the elements. Their
molecules can be separated back into the elements
that they are made of, or other, but simpler,
compounds.
Chemical Bonding
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Two types of bonding
– Ionic bonding
– Covalent bonding
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Ionic bonding occurs when 1 atom
donates 1/more electrons to another atom
– DONATE electrons
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Covalent bonding atoms combine to
share electrons to fulfill the octet rule.
– SHARE electrons
Ionic Bonding
In ionic bonding, electrons are completely transferred from one atom to another. In the
process of either losing or gaining negatively charged electrons, the reacting atoms form
ions. The oppositely charged ions are attracted to each other by electrostatic forces, which
are the basis of the ionic bond.
For example, during the reaction of sodium with chlorine:
sodium (on the left) loses its
one valence electron to
chlorine (on the right),
Resulting in a positively
charged sodium ion (left) and
a negatively charged chlorine
ion (right).
Notice that when sodium loses its one valence electron it gets
smaller in size, while chlorine grows larger when it gains an
additional valence electron. This is typical of the relative sizes of
ions to atoms. Positive ions tend to be smaller than their parent
atoms while negative ions tend to be larger than their parent.
After the reaction takes place, the charged Na+ and Cl- ions are
held together by electrostatic forces, thus forming an ionic bond.
Ionic compounds share many features in common:
Ionic bonds form between metals and nonmetals.
In naming simple ionic compounds, the metal is always first, the
nonmetal second (e.g., sodium chloride).
Ionic compounds dissolve easily in water and other polar solvents.
In solution, ionic compounds easily conduct electricity.
Ionic compounds tend to form crystalline solids with high melting
temperatures.
Ionic Bonds
Where covalent bonds involve shared electrons, "ionic bonds" are formed when one
atom gives up an electron from an outer shell (orbital) and the other atom adds the free
electron to its outer most orbital, thereby holding the atoms together in an energetically
stable unit.
When an atom loses an electron it would have one more positively charged proton (+)
then electrons, therefore, the atom would be carrying an overall net charge of (1+). When
an atom gains and electron it contains one more electron than protons and therefore
would be carrying a net charge of (1-). Atoms which have gained or lost electrons are
called ions. Ions are charged, atoms or molecules. Anions carry a negative charge eg.
(Cl-) while cations carry a positive charge (Na+).
The strong attraction between positive and negative ions gives rise to and ionic bond. For
example the ionic bond between sodium and chlorine (sodium chloride, common table
salt).
Table salt
Sodium has only one electron in its outer-most orbital, therefore, it can
achieve the more energetically stable arrangement of a "full outer"
shell by losing the lone outer electron. Chlorine on the other hand has
seven electrons in its outermost shell, and it can achieve the
energetically stable arrangement of a full outer shell by gaining the
electron from sodium.
Therefore, the atoms of sodium become positively charged cations and
the atoms of chlorine become negatively charged anions and these are
held together by ionic bonds as "sodium chloride" (NaCl) (table salt).
Covalent Bonding
The second major type of atomic bonding occurs when atoms share
electrons.
As opposed to ionic bonding in which a complete transfer of electrons
occurs, covalent bonding occurs when two (or more) elements share
electrons.
Covalent bonding occurs because the atoms in the compound have a
similar tendency for electrons (generally to gain electrons).
This most commonly occurs when two nonmetals bond together. Because
both of the nonmetals will want to gain electrons, the elements involved
will share electrons in an effort to fill their valence shells.
A good example of a covalent bond is that which occurs between two
hydrogen atoms. Atoms of hydrogen (H) have one valence electron in their
first electron shell.
Since the capacity of this shell is two electrons, each hydrogen atom will
"want" to pick up a second electron. In an effort to pick up a second
electron, hydrogen atoms will react with nearby hydrogen (H) atoms to
form the compound H2.
Because the hydrogen compound is a combination of equally matched
atoms, the atoms will share each other's single electron, forming one
covalent bond. In this way, both atoms share the stability of a full valence
shell.
The unfilled orbitals of four hydrogen can form four covalent bonds by a sharing
of pairs of electrons between carbon and hydrogen.
Atoms that have the same number of protons but different numbers of
neutrons are called isotopes. The element hydrogen, for example, has
three commonly known isotopes: protium, deuterium and tritium.
CW: FCAT Book Pp.65-66
 In
your NOTEBOOK
 Answer questions 30-34
 Write out questions/tables
 Work on your own QUIETLY!!!!!
 Will be discussed and graded