Partielo | Science

Definitions

Atom

An atom is the smallest unit of matter that retains the properties of an element. It consists of a nucleus made of protons and neutrons, surrounded by electrons.

Element

A pure substance consisting of only one type of atom, characterized by its atomic number.

Atomic Number

The number of protons in the nucleus of an atom; it defines the element.

Mass Number

The total number of protons and neutrons in an atom's nucleus.

Atomic Mass Unit (AMU)

A unit to measure atomic mass. 1 AMU is 1/12 the mass of a carbon-12 atom, approximately equal to the mass of a proton or neutron.

1. The Structure of an AtomAtoms are the building blocks of matter, comprising a nucleus of protons and neutrons, with electrons orbiting in energy levels. The structure determines the atom's chemical behavior and properties.

2. Atomic Number and Mass Number"Atomic number" denotes the number of protons in an atom, uniquely identifying an element. In a neutral atom, electrons equal protons. "Mass number" is the sum of protons and neutrons, providing the atomic mass. The formula is: Mass number = No. of Protons + No. of Neutrons.

3. Electronic ConfigurationThe electronic configuration describes how electrons are distributed in the atom's energy shells or orbitals. For example, oxygen (atomic number 8) has 8 electrons arranged as 2 in the first shell and 6 in the second, written as 2, 6.

4. The Periodic TableIt is a chart arranging all known chemical elements based on increasing atomic number. It provides a systematic way to understand the properties and relationships between elements.

Periods and Groups

5. Periods (Rows)Rows in the periodic table are called periods; there are 7. Elements in the same period have the same number of electron shells, and properties tend to change gradually across a period.

6. Groups (Columns)Columns are called groups; there are 8 main groups. Elements in the same group have a similar number of electrons in their outermost shell, leading to similar chemical properties.

Trends in the Periodic Table

7. Melting and Boiling PointsWithin a period, melting and boiling points generally increase from metals to transition metals, with non-metals typically having low points. Exceptions include diamond (carbon), which has a high melting point. Down a group, melting points in groups 1 and 2 decrease, while in halogens and noble gases, they tend to increase.

8. HardnessHardness measures an element’s resistance to deformation or scratching. Across a period, hardness generally increases; alkali metals are exceptions as they are soft. Down the group, hardness decreases in groups 1 and 2.

9. Colour and AppearanceMetals are usually silvery grey but can have other colours, such as copper and gold. Non-metals are often colourful, and metalloids display intermediate properties with colours like grey or black.

To remember :

In summary, the periodic table organizes all known elements based on atomic number, revealing trends such as changes in melting point, hardness, and color across periods and groups. Atoms, the fundamental units of matter, are composed of protons, neutrons, and electrons. The arrangement of electrons around the nucleus defines the element's chemical properties. Understanding these concepts allows us to comprehend the behavior of elements and predict their interactions.