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The concept of mole is extremely useful in chemistry. The mole is a term like dozen. Dozen means 12. The mole means 6.02 x 1023. It is convenient for chemists to use a concept like mole which represents such a large number since they deal in very small and very numerous quantities. The mole is also called Avogadro’s number. Avogadro’s …

There are two types of compounds: molecular and ionic compounds. For molecular compounds, a molecular formula represents the number and kinds of atoms in the molecule. The molecular formula also tells us the lowest whole number ratio between the atoms in the compound. For example, water is represented by the formula H2O. This formula indicates that in every water molecule, there …

Compounds Compounds are pure substances that differ from elements because they contain more than one kind of atom. The Law of Definite Composition (or the Law of Definite Proportions) applies to compounds. For example, sodium chloride contains one atom of sodium for each atom of chlorine. Water contains two atoms of hydrogen for each atom of oxygen. It is known …

Isotopes: Isotopes are atoms of the same element having the same atomic number but different atomic masses. Note that the difference in the masses of isotopes is due to the different number of neutrons in their nuclei. Isotopes have the same chemical properties . because they have the same number of electrons. Isotopes have different physical properties because they have different …

Atomic Number: Atomic number of an element is equal to the number of protons present in the nucleus of an element. Atomic number = number of protons in one atom of element. Since the atom as a whole is neutral therefore atomic number is the same as the number of electrons around the nucleus of an atom. Atomic number of …

Each atom is made up of an inner core called the nucleus.  – Most of the atom’s mass is located in the relatively small nucleus.  – The rest of the atom is comprised of a relatively large region outside the nucleus where the electrons are found. – The atom is made of 3 subatomic particles: Positively charged protons Neutral particles …

Dalton’s Model of the atom. It is the basis of our understanding of the nature of matter. The following four statements comprise Dalton’s Model: a –  All matter is made up of extremely tiny. particles. called atoms. b-  Atoms are indivisible. c – Atoms of the same element are alike. d –  Atoms of different elements are different. e – …

The law of Conservation of Mass states that the mass of matter before and after a chemical change remains the same. The number of atoms also remains the same. The only thing that changes is the arrangement of the atoms. For example, the mass of hydrogen and oxygen before they combine to make water is the same as the mass …

Like matter, energy can be classified in different ways. For example, energy can either be kinetic or potential. Kinetic energy is energy of motion. Gases are made of molecules that have more kinetic energy than molecules in the solid phase of that substance. For example, water molecules in steam have greater kinetic energy than molecules in liquid water. Potential energy …

Substances can undergo three type of changes: – Physical changes – Chemical changes (also known as chemical reactions) – Nuclear changes (also known as nuclear reactions) In a physical change the appearance (color, shape, etc.) of the substance may change, but the substance will remain the same substance. A phase change is an example of a physical change. For example, …