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Atomic Structure
What are atoms??
The structure of an atom
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Matter has mass and takes up space
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Atoms are basic building blocks of
matter, and cannot be chemically
subdivided by ordinary means
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The word atom is derived from the
Greek word atom which means
indivisible

The Greeks concluded that matter could
be broken down into particles to small to
be seen. These particles were called
atoms
Atoms are composed of three
type of particles: protons,
neutrons, and electron
•Protons and neutrons are
responsible for most of the
atomic mass
•The mass of an electron is
very small
•Both the protons and
neutrons reside in the nucleus.
•Protons have a postive (+)
charge
•Neutrons have no charge -they are neutral.
•Electrons reside in orbitals
around the nucleus. They have
a negative charge (-).
Sum it up:

Protons
– positive charge
– mass of 1
– located in the nucleus

Neutrons
– neutral
– mass of 1
– located in nucleus
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Electrons
– negative charge
– mass of 0
– located in region
outside of the
nucleus
•Electrons are found in clouds that surround the
nucleus of an atom.
•Because electrons move so quickly, it is impossible
to see where they are at a specific moment in time.
•After years of experimentation, scientists
discovered specific areas where electrons are likely
to be found. These shells change depending on how
many electrons an element has.
• The higher the atomic number, the more shells and
electrons an atom will have.
ORBITAL BASICS

Let's cover some basics of atomic orbitals.
1. A shell is sometimes called an orbital or energy level.
2. Shells are areas that surround the center of an atom.
3. The center of the atom is called the nucleus.
4. Electrons live in something called shells.
5. Each of those shells has a name.
There are a couple of ways that atomic orbitals are named. You
may have heard of the SPDF system before. Chemists also use
letters to name the orbitals around a nucleus. They use the
letters "k,l,m,n,o,p, and q". The "k" shell is the one closest to the
nucleus and "q" is the farthest away.
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Not all shells hold the same number of
electrons. For the first eighteen elements,
there are some easy rules.
The k-shell only holds two electrons.
The l-shell only holds eight electrons.
The m-shell only holds eight electrons (for the
first eighteen elements).
The maximum number of electrons you will
find in any shell is 32.
Important Definitions
Atoms, atomic structure, chemical
bonding, etc.
atom The smallest indivisible particle of matter that can
have an independent existence.
atomic number The number of protons in the nucleus
of an atom.
atomic weight The sum of the weights of an atom's
protons an neutrons, the atomic weight differs between
isotopes of the same element.
neutron An uncharged subatomic particle in the nucleus
of an atom. The large (mass approximately equal to 1
atomic mass unit), electrically neutral particle that may
occur in the atomic nucleus.
electron A subatomic particle with a negative charge.
Electrons circle the atom’s nucleus in regions of space
known as orbitals.
element A substance composed of atoms with the same
atomic number; cannot be broken down in ordinary
chemical reactions.
proton A subatomic particle in the nucleus of an atom that
carries a positive charge. The positively charged (+1)
subatomic particle located in the nucleus and having a mass
slightly less than that of a neutron. Electron differ by the
number of protons in their atoms.
molecules Units of two or more atoms held together by
chemical bonds. The combination of atoms by chemical
bonds with the component atoms in definite proportions,
such as water (two H to one O).
matter Anything that has mass and occupies space.
ionic bond A chemical bond in which atoms of opposite
charge are held together by electrostatic attraction.
isotonic Term applied to two solutions with equal solute
concentrations.
isotopes Atoms with the same atomic number but
different numbers of neutrons; indicated by adding the
mass number to the element's name, e.g., carbon 12 or 12C.
nucleus (atom) An atom's core; contains protons and one
or more neutrons (except hydrogen, which has no
neutrons).
radioactive decay The spontaneous decay of an atom to
an atom of a different elements by emission of a particle
from its nucleus (alpha and beta decay) or by electron
capture.
covalent bond A chemical bond created by the sharing of
electrons between atoms.
ionic bond A chemical bond in which atoms of opposite
charge are held together by electrostatic attraction.
isotopes Atoms with the same atomic number but
different numbers of neutrons; indicated by adding the
mass number to the element's name, e.g., carbon 12 or 12C.
Review Questions
•Which of these is not a subatomic particle? a) proton; b) ion;
c) neutron; d) electron
•The outermost electron shell of every Noble Gas element
(except Helium) has ___ electrons. a) 1; b) 2; c) 4; d) 6; e) 8
•An organic molecule is likely to contain all of these elements
except ___. a) C; b) H; c) O; d) Ne; e) N
•The chemical bond between water molecules is a ___ bond.
a) ionic; b) polar covalent; c) nonpolar covalent; d) hydrogen
•A solution with a pH of 7 has ___ times more H ions than a
solutrion of pH 9. a) 2; b) 100; c) 1000; d) 9; e) 90
•The type of chemical bond formed when electrons are shared
between atoms is a ___ bond. a) ionic; b) covalent; c)
hydrogen
•The type of chemical bond formed when oppositely
charged particles are attrached to each other is a ___ bond.
a) ionic; b) covalent; c) hydrogen
•Electrons occupy volumes of space known as ___. a)
nuclei; b) periods; c) wavelengths; d) orbitals
•Carbon has an atomic number of 6. This means it has ___.
a) six protons; b) six neutrons; c) six protons plus six
neutrons; d) six neutrons and six electrons
•Each of the isotopes of hydrogen has ___ proton(s). a) 3;
b) 1; c) 2; d) 92; e) 1/2
•A molecule is ___. a) a mixture of various components that
can vary; b) a combination of many atoms that will have
different ratios; c) a combination of one or more atoms that
will have a fixed ratio of its components; d) more important
in a chemistry class than in a biology class