Basic Chemistry
1.  Atomic Structure
Matter has mass and takes up space. Atoms are basic building blocks of matter, and cannot be chemically subdivided by ordinary means.
Both the protons and neutrons reside in the nucleus. Protons have a positive (+) charge, neutrons have no charge --they are neutral. Electrons reside in orbitals around the nucleus. They have a negative charge (-).
It is the number of protons that determines the atomic number. The number of protons in an element is constant but neutron number may vary, so mass number (protons + neutrons) may vary.
The same element may contain varying numbers of neutrons; these forms of an element are called isotopes. The chemical properties of isotopes are the same, although the physical properties of some isotopes may be different. Some isotopes are radioactive-meaning they "r
adiate" energy as they decay to a more stable form, perhaps another element half-life: time required for half of the atoms of an element to decay into stable form. Another example is oxygen, with atomic number of 8 can have 8, 9, or 10 neutrons.
Here is a list of the basic characteristics of atoms:
● An atom is a basic chemical building block of matter. Atoms cannot be divided using chemicals. They do consist of parts, which include protons, neutrons, and electrons, but an atom is a basic chemical building block of matter.
● Each electron has a negative electrical charge.
● Each proton has a positive electrical charge. The charge of a proton and an electron are equal in magnitude, yet opposite in sign. Electrons and protons are electrically attracted to each other.
● Each neutron is electrically neutral. In other words, neutrons do not have a charge and are not electrically attracted to either electrons or protons.
● Protons and neutrons are about the same size as each other and are much larger than electrons. The mass of a proton is essentially the same as that of a neutron. The mass of a proton is 1840 times greater than the mass of an electron.
● The nucleus of an atom contains protons and neutrons. The nucleus carries a positive electrical charge.
● Electrons move around outside the nucleus.
● Almost all of the mass of an atom is in its nucleus; almost all of the volume of an atom is occupied by electrons.
● The number of protons (also known as its atomic number) determines the element. Varying the number of neutrons results in isotopes. Varying the number of electrons results in ions. Isotopes and ions of an atom with a constant number of protons are all variations of a single element.
● The particles within an atom are bound together by powerful forces. In general, electrons
are easier to add or remove from an atom than a proton or neutron. Chemical reactions largely involve atoms or groups of atoms and the interactions between their electrons.
2. Chemical Bonding
Atoms are the basic building blocks of all types of matter. Atoms link to other atoms through chemicals bonds resulting from the strong attractive forces that exist between the atoms.
So what exactly is a chemical bond? It is a region that forms when electrons from different atoms interact with each other. The electrons that participate in chemical bonds are the valence electrons, which are the electrons found in an atom's outermost shell. When two atoms approach each other these outer electrons interact. Electrons repel each other, yet they are attracted to the protons within atoms. The interplay of forces results in some atoms forming bonds with each other and sticking together.
⑴reaction mass Ionic bonds
Ionic bonds arise from elements with low electronegativity (almost empty outer shells) react
ing with elements with high electronegativity (mostly full outer shells). In this case there is a complete transfer of electrons. 
A well known example is table salt, sodium chloride. Sodium gives up its one outer shell electron completely to chlorine which needs only one electron to fill its shell. Thus, the attraction between these atoms is much like static electricity since opposite charges attract.
⑵ Covalent bond
Covalent bonds involve a complete sharing of electrons and occurs most commonly between atoms that have partially filled outer shells or energy levels. Thus if the atoms are similar in negativity then the electrons will be shared. Carbon forms covalent bonds. The electrons are in hybrid orbitals formed by the atoms involved as in this example: ethane. Diamond is strong because it involves a vast network of covalent bonds between the carbon atoms in the diamond.
⑶ Polar Covalent Bond. 
These bonds are in between covalent and ionic bonds in that the atoms share electrons but the electrons spend more of their time around on atom versus the others in the compound. This type of bond occurs when the atoms involved differ greatly in electronegativity. The most familiar example is water. Oxygen is much more electronegative than hydrogen, and so the electrons involved in bonding the water molecule spend more time there.

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