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- An ion is formed when an atom looses electron from its outer shell or gains electrons in its outer shell.
- Ions are not electrically neutral because the number of electrons and number of protons are not same.
- An ion of an element can be either positive or negative. Positive Ions are called cations and negative Ions are called anions. For example ion of Oxygen is O-2 and ion of Sodium is Na+.
- The ionic radius of a cation is always less than the atomic radius of that parent atom. For example ionic radius of Na+ is 1.02 Angstrom and atomic radius of Na is 1.57 Angstrom.
- The ionic radius of an anion is always greater than the atomic radius of the parent atom. For example ionic radius of O-2 is 1.40 Angstrom and atomic radius of O is 0.73 Angstrom.
- Compounds are pure substances and always homogeneous by nature.
- A compound is formed when two or more elements reacts chemically in a fixed proportion by mass. For example NaOH, NaCl and HCl are compounds.
- Every particles of a compound are alike and show same characteristics.
- Constituent elements of a compound can be separated only by chemical means.
- A compound has a definite set of physical and chemical properties which are different from its constituent elements.
- When two or more elements join chemically a compound is formed which is a whole new substance.
- Every solid matter has definite volume and shape. Because inter particle attractions between particles is maximum.
- Solids are highly rigid. Because the space between the particles of a solid are negligible.
- A solid matter cannot flow. Because the particles of solids have least kinetic energy.
- Solids have highest density because of negligible gap between particles.
- Solids are almost incompressible. Due to negligible gap between particles.
- A solid can have any number of surfaces.
- Solids don’t apply any pressure.
- An element is pure substance formed by same kind of atoms (Having same atomic numbers). Examples of elements are Hydrogen, Oxygen, Carbon, Iron, Sodium etc.
- There are only 118 elements in the world. Thus number of elements in the world is limited.
- An element can’t be broken down into two or more simpler substances by any method.
- Every element has a unique atomic number. Thus different elements can’t have same atomic number. For example of atomic number of hydrogen is 1.
- Every element possess some physical and chemical properties.
- A physical change is a kind of change in which no new substance is formed. This is the main property of a physical change. For example melting of ice is a physical change because here water changes its state from solid to liquid.
- It is a temporary change. If we remove the cause of change then the substance will regain its original state. For example when some sugar is dissolved in water, the state of sugar is changed. But if we heat the sugar solution until the whole water is evaporated then we get the sugar back in crystalline form.
- In a physical change, neither energy is evolved nor energy is absorbed.
- The total weight of a substances is same before and after the physical change.
- The chemical properties and composition of the substance do not alter during physical change.
- Alterations in shape, size, volume, physical state, colour and processes like melting, evaporation, condensation, freezing, distillation expansion, contraction, cooling, heating, rain cycle, drying of fruits, magnetization, ringing of electeical bell, sublimation all are physical change.
- An atom is the smallest particle of an element that can be further decomposed into subatomic particles. These subatomic particles are electron, proton and neutron. Example of atoms are Hydrogen (H), Carbon (C), Sulphur (S) and Iron (Fe).
- Atoms of an element take part into chemical reactions without further decomposition into subatomic particles.
- An Atom of an element can not be free state.
- Atoms can loose and gain electrons to form ions. If an atom Looses electronic then it becomes positive ion. And if it gains electron then it becomes negative ion.
- Mass of an atom cannot be determined practically.
- Cations are positively charged ions. Examples of Cations are Na+, Mg+2 and Al+3.
- Cations are formed by the loss of one or more electrons from the outer shell or orbit of atoms to achieve their octet or duplet.
- Number of electron in a cation is less than the number of proton in that cation. For example Na+ has 10 elections and 11 protons.
- Ionic radii of cations decrease with increase in positive charges. For example Ionic radius of Na+ is more than that of Mg+2.
- Ionic size of a cation is always smaller than its parent atom. Because effective nuclear charge increases. For example Ionic size K+ is less than atomic size of K.
- Cations are ions of metals.
- Anions are negatively charged ions. Examples of Anions are F–, O-2 and N-3.
- An anion is formed by gaining one or more electrons in their valence shell to complete their octet or duplet.
- Number of electrons in an anion is more than the number of protons in it. For example Cl has 17 electrons as well as 17 proton but Cl– has 18 electrons and 17 protons.
- Ionic radii of anion increase with decrease in negative charges. Thus Cl– will have higher Ionic radius than that of S-2.
- Ionic size of anions are larger than their parent atoms. Because effective nuclear charge decreases. Ionic size of Cl– is larger than atomic size of Cl.
- Anions are ions of non-metals.