The basics concept of chemistry | What is Atom? Characteristics of atoms? What are the types of chemical bond?

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CHEMISTRY is the science and study of matter, including its properties, composition as well as reactivity. Chemistry relates to everything that can be sensed from the minutes elements to complex structures. The atom and molecules are the Basic units or components of chemistry.


Atom:

All matter consists of particles known as an atom. Atoms bond to each other to form elements, which contain only one kind of atom. Atoms of different elements form compounds, molecules, and objects.

Model of the atom:

  • An atom is a building block of matter that can not be broken apart using any chemical means.
  • The 3 parts of the atoms are protons (positively charged), neutrons (neutral charged), and electrons (negatively charged).
  • Proton and neutron form the NUCLEUS. Electrons are attracted to the protons in the nucleus but are moving quickly they fall toward orbit rather than stick to protons.
  • The identity of an atom is determined by it's no. of protons. This is also called its atomic number.

PARTS OF AN ATOM:

An atom consists of 3 parts:
1.Protons: Protons are the basis of atoms. While an atom can gain or loss neutron and electrons, its identity is tied to the number of protons. The symbol for proton number is the capital letters Z.

2. Neutrons: The number of neutrons in an atom is indicated by the letter N. The atomic mass of an atom is the sum of its protons and neutrons or Z+N. The strong nuclear force binds protons and neutrons together to form the nucleus of an atom. 

3. Electrons: Electrons are much smaller than protons or neutrons and orbit around them. 

Characteristics of atoms:

  • Each electron has a negative electrical charge. 
  • Each proton has a positive electrical charge. The charge of proton and an electron are equal in magnitude. Electrons and protons are electrically attracted to each other. 
  • The nucleus of an atom contains protons and neutrons. The nucleus carries a positive electrical charge. 
  • Atoms are very small. The average size of an atom is about 100 pico meters or one ten billionth of a meter. 
  • 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 particles within a 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 involves atoms or groups of atoms and the reactions between their electrons.
ATOMIC MASS and ATOMIC MASS NUMBER:
Atomic mass and atomic mass number are two important concept in chemistry. Here a review of what is meant by atomic mass and atomic mass number.

ATOMIC MASS:
  • Z is used to signify the atomic number or proton number of an atom.
  • A is used to signify the atomic mass number. 
  • A and Z are integer values. 
  • When the actual mass of an atom is expressed in amu (atomic mass units) or g/mol then the value is close to A. 

Types of Chemical Bonds:

A chemical bond is a region that forms when electrons from different atoms interact with each other. The electrons that participate in chemical bonds are the valance electrons, which are the electrons found in an atom's outermost shell. When two atoms approach each other these outer electrons interact. Electron 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. 

Main Types of Chemical Bond:

The two main types of bonds formed between atoms are ionic bonds and covalent bonds. An ionic bond is formed when one atom acceptor donate one or more of its valence electrons to another atom. A covalent bond is formed when atoms share valence electrons. The atom do not always share the electrons equally, so a polar covalent bond may be the result. When electrons are shared by two metallic atoms a metallic bond may be formed. 

IONIC BOND:

In an ionic bond, one atom is essentially donates an electron to stabilize the other atom. In other words, the electron spends most of its time close to the bonded atom. Atoms that participate in an ionic bond have different electronegativity values from each other. A polar bond is formed by the attraction between oppositely-charged ions. 

For e.g. Sodium and chloride form an ionic bond, to make NaCl. 

COVALENT BOND:

 
In a covalent bond, the atoms are bound by shared electrons. In a true covalent bond, the electronegativity values are the same (e.g. H2) although in practice the electronegativity values just need to be close. If the electrons are shared equally between the atoms forming a covalent bond, then the bond is said to be non polar. Usually, an electron is more attracted to one atom than to another, forming a covalent bond.for e.g. The atom in a water(H2O) are held together by covalent bonds.


States of matter:

 

Matter occurs in four states: Solids, liquids, gases, and plasma. Often the state of matter of a substance may be changed by adding or removing heat energy from it. For e.g. The addition of heat can melt ice into liquid water and turn water into steam. 

SOLIDS:
A solid has a definite shape and volume because the molecules that make up the solid are packed closely together and move slowly. Solids are often crystalline; examples of crystalline solids include  table salt, sugar, diamonds, and many other minerals. Other e.g. of solids include wood, metal.

LIQUIDS:
A liquid has a definite volume but takes the shape of its container. Examples of liquids include water and oil. Gases may liquefy when they cool, as is the case with water vapor. This occurs as the molecules in the gas slow down and loss energy. 

GASES:
A gas has neither a definite volume nor a definite shape. Some gases can be seen and felt, while others are intangible for human beings. Examples of gases are air, oxygen, helium. Earth atmosphere is made up of gases  including oxygen, nitrogen, carbon dioxide. 

PLASMA:
Plasma has neither a definite volume nor a definite shape. Plasma often is seen in ionized gases, but it is distinct from a gas because it possesses unique properties. Examples of plasma include stars, lightnings etc. 

ACIDS AND BASES:

Arrhenius Acids and Bases:

According to Arrhenius theory-
  • Acids produce H+ ions in aqueous solutions
  • Bases produces OH- ions in aqueous solutions
  • Water required, so only allows for aqueous solutions
  • Only protic acids are allowed: required to produced hydrogen ions
  • Only hydroxide bases are allowed

Lowry-Bronsted Acids and Bases:

According to Lowry-Bronsted theory-
  • Acids are proton donors
  • Bases are proton acceptors
  • Aqueous solutions are permissible
  • Bases besides hydroxides are permissible
  • Only protic acids are allowed

Lewis Acids and Bases:

According to Lewis theory-
  • Acids are electron pair acceptors  
  • Bases are electron pair donors
  • Least restrictive of the acid-base definitions
 
 

 








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