Grade 11 elite Biology
Chemistry Review
Matter: refers to anything that takes up space and has mass.
Element: is a substance that cannot be broken down to simpler substances by
ordinary chemical means, and it’s both non-living and living.
Atoms: are the smallest part of an element that displays the same properties.
Atomic number: the number of protons in the nucleus.
Mass number: the sum of the protons and neutrons in the nucleus.
The three best-known subatomic particles are:
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positively charged protons
uncharged neutrons
negatively charged electrons.
Protons and neutrons are located within the nucleus of an atom, and electrons
move about the nucleus.
Done by Dr.Abed alfatah Alhawamdeh
WhatsApp number: 00962790836453
periodic table: is a tabular arrangement of the chemical elements by
increasing atomic number.
Groups: The vertical column of the periodic table that signifies the number of
valence electrons in an element, Each atom in a group within the periodic table
has the same number of electrons in its valence shell.
Periods: The horizontal rows in the periodic table that signify the number of
electron shells in an element.
Isotopes: are atoms of the same element that differ in the number of
neutrons.
Changing the number of neutrons can make the nucleus less stable and so it
breaks apart, as it breaks apart it releases radiation that can be detected.
For example, the element carbon has three naturally occurring isotopes:
Radioactive Isotopes
Some isotopes of an element are unstable, or radioactive and called
Radioactive Isotopes. for example, carbon 14.
1- Low Levels of Radiation:
The chemical behaviour of a radioactive isotope is essentially the same as that
of the stable isotopes of an element. This means that you can put a small
amount of radioactive isotope in a sample and it becomes a tracer by which to
detect molecular changes and can be used to detect tumours.
Onther example of low levels of radiation uses is Positron-emission
tomography (PET) scans can be used to detect coronary artery disease and
memory disorders like Alzheimer's.
Done by Dr.Abed alfatah Alhawamdeh
WhatsApp number: 00962790836453
2- High Levels of Radiation:
Radioactive substances in the environment can harm cells, damage DNA, and
cause cancer.
This Radiation can be used for good to sterilize hospital and dental
equipment. High radiation can also be used to kill cancer cells.
Electrons and Energy
One of the more common models of atoms is the Bohr model, developed by
the physicist Niels Bohr (1885–1962).
In Bohr models of atom Electrons orbit the nucleus at particular energy levels
(electron shells). The first shell contains up to two electrons, and thereafter
each shell is most stable when it contains 8 electrons. Atoms with an atomic
number above 20 may have more electrons in their outer shells. The
outermost, or valence, shell helps determine the atom’s chemical properties
and how many other elements it can interact with.
Because the negatively charged electrons are attracted to the positively
charged nucleus, it takes energy to push them away and keep them in their
own shell. The more distant the shell, the more energy it takes.
valence shell: the outermost shell.
The valence shell is important, because it determines many of an atom’s
chemical properties. If an atom has only one shell, the valence shell is
complete when it has two electrons. In atoms with more than one shell, the
valence shell is most stable when it has eight electrons. This is called the octet
rule.
The electrons in the valence shells play an important role in determining how
an element undergoes chemical reactions. Atoms with fewer than eight
electrons in the outer shell react with other atoms in such a way that after the
reaction each has a stable outer shell. As we will see, the number of electrons
in an atom’s valence shell determines whether the atom gives up, accepts, or
shares electrons to acquire eight electrons in the outer shell.
Molecules and Compounds
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molecule exists when two or more elements bond together.
compound: is a molecule containing at least two different elements.
Ion: an atom that has a charge because it has lost or gained an electron.
Ionic bonding: ionic compounds are held together by an attraction
between negatively and positively charged ions.
➢ Covalent bonds: a covalent bond is a type of chemical bond
characterized by the joint sharing of electron pairs between atoms.
Covalent bonds form when atoms share valence electrons with other
atoms to achieve a full shell of outer electrons.
Done by Dr.Abed alfatah Alhawamdeh
WhatsApp number: 00962790836453
Nonpolar and Polar Covalent Bonds
➢ Nonpolar covalent bonds: this is when the sharing of electrons between
two atoms is equal.
➢ Electronegativity: this is when one atom is able to attract electrons to a
greater degree than the other atom.
➢ Polar covalent bonds: these are covalent bonds where the electrons are
not shared equally
Done by Dr.Abed alfatah Alhawamdeh
WhatsApp number: 00962790836453