LAB 2: ATOMIC STRUCTURE AND THE PERIODIC TABLE

Background of the Experiment:

Atom, smallest unit into which matter can be divided without the release of electrically charged

particles. It also is the smallest unit of matter that has the characteristic properties of a chemical

element. As such, the atom is the basic building block of chemistry.

Atomic structure refers to the structure of an atom comprising a nucleus (center) in which the

protons (positively charged) and neutrons (neutral) are present. The negatively charged

particles called electrons revolve around the center of the nucleus.

Most of the atom is empty space. The rest consists of a positively charged nucleus of protons

and neutrons surrounded by a cloud of negatively charged electrons. The nucleus is small and

dense compared with the electrons, which are the lightest charged particles in nature. Electrons

are attracted to any positive charge by their electric force; in an atom, electric forces bind the

electrons to the nucleus.

The protons and neutrons make up the nucleus of the atom, which is surrounded by the

electrons belonging to the atom. The atomic number of an element describes the total number of protons in its nucleus.

Because of the nature of quantum mechanics, no single image has been entirely satisfactory at

visualizing the atom’s various characteristics, which thus forces physicists to use

complementary pictures of the atom to explain different properties. In some respects, the

electrons in an atom behave like particles orbiting the nucleus. In others, the electrons behave

like waves frozen in position around the nucleus. Such wave patterns, called orbitals, describe

the distribution of individual electrons. The behavior of an atom is strongly influenced by these

orbital properties, and its chemical properties are determined by orbital groupings known as

shells.

Dalton’s Atomic Theory

The English chemist John Dalton suggested that all matter is made up of atoms, which were

indivisible and indestructible. He also stated that all the atoms of an element were exactly the

same, but the atoms of different elements differ in size and mass.

Chemical reactions, according to Dalton’s atomic theory, involve a rearrangement of atoms to

form products. According to the postulates proposed by Dalton, the atomic structure comprised

atoms, the smallest particle responsible for the chemical reactions to occur.

The following are the postulates of his theory:

∙ Every matter is made up of atoms.

∙ Atoms are indivisible.

∙ Specific elements have only one type of atoms in them.

∙ Each atom has its own constant mass that varies from element to element. ∙

Atoms undergo rearrangement during a chemical reaction.

∙ Atoms can neither be created nor be destroyed but can be transformed from one form to