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Elements, Compounds and mixtures
Element.A substance that cannot be broken down into simpler substances by chemical means. An element is composed of atoms that have the same atomic number, that is, each atom has the same number of protons in its nucleus as all other atoms of that element.
What is the classification of elements on the basis of properties?
Ans: Based on the properties, elements are classified into 3 types. They are metals, non-metals and metalloids.
Why do we classify elements?
Ans: Scientists gained more knowledge on the properties of new elements as they were found. It was discovered that organizing all of the information or properties of these elements was difficult. As a result, scientists began to look for patterns in their properties in order to classify all of the known elements and make their research easier.
What are Metals?
78% of known elements are metals.
They take up the left side of the Periodic Table.
At room temperature, they are usually solids (except mercury).
They usually have high boiling and melting points.
They are shiny having a metallic lustre.
They are good conductors of heat and electricity.
They are malleable, that is, they can be hammered into thin sheets.
They are ductile, that is, they can be drawn into wires.
All the metals tend to lose electrons easily.
What are Non- Metals?
They occupy the right-hand side of the Periodic Table.
Most non-metals are brittle and are not malleable or ductile.
At room temperature, they are usually gases.
They usually have low boiling and melting points (except for carbon and boron).
They are poor conductors of heat and electricity.
They are usually less dense when compared to metals.
They tend to gain electrons during chemical reactions.
What are Metalloids?
Metalloids exhibit some properties of metals as well as non-metals. Hence, they are also known as semi-metals.
Boron, silicon, germanium, arsenic, antimony, and tellurium are the most commonly recognized metalloids.
These elements run diagonally across the Periodic Table.
They may have a metallic or dull appearance.
They are usually brittle and are fair conductors of electricity.
They may gain or lose electrons during chemical reactions.
They form alloys with metals.
They are used as catalysts, biological agents, flame retardants, alloys and semiconductors in industries due to their unique properties
118 Elements and Their Symbols and Atomic Numbers
What is a Compound?
When two or more elements chemically combine in a fixed ratio by mass, the obtained product is known as a compound. Compounds can be defined as substances consisting of 2 or more different types of elements in a fixed ratio of their atoms. When the elements combine, some individual property of the elements is lost and the newly formed compound has new properties.
Chemical Formula: Compounds are represented by their chemical formula. A chemical formula is a symbolic representation of the proportions of atoms that constitute a particular chemical compound.
The chemical formula of water is H2O which shows two atoms of hydrogen and one atom of oxygen have combined to form one molecule of H2O. The chemical formula for common salt is NaCl which shows one atom of sodium and one atom of chlorine combine to form one molecule of NaCl.
1. Types Of Compounds
Compounds can be classified into two types, molecular compounds and salts. In molecular compounds, the atom binds each other through covalent bonds. In salts, it is held together with ionic bonds. These are the two types of bonds out of which every compound is made of.
2. Example Of Compounds
Example of compounds includes water (H2O), Hydrogen Peroxide (H2O2), etc. You could see water’s chemical formula, it says it has 2 atoms of Hydrogen combined with 1 atom of oxygen and in hydrogen peroxide, it has 2 atoms of hydrogen and two atoms of oxygen.
Similarly, an example of salt would be the table salt (NaCl) which has 1 atom of sodium and one atom of chlorine.
Examples of some commonly used compounds and their molecular formula:
Mixture
In chemistry, when two or more substances mix with each other without participating in a chemical change, the resulting substance is called a Mixture
Characteristics of Mixtures
The constituents of a mixture are not present in a fixed ratio. The various characteristics of mixtures are discussed below.
There is no chemical force acting between the two or more substances that are mixed, but they still exist together.
They can either be heterogeneous or homogeneous in nature.
The proportions of the substances vary in an indefinite manner.
The properties of the mixture depend upon the individual components.
The constituents of the mixture can be separated by physical methods.
The boiling point and the melting point of the mixture depends upon the characteristic of the constituents.
During the formation of a mixture, there is no change in energy.
All the states of matter (solid, liquid, gases) can combine to form mixtures.
It can be concluded that almost everything in our vicinity is nothing but a mixture. For example, the food we eat is a mixture of ingredients, the atmospheric air we breathe is a combination of gases and the fuel we use in locomotives is a heterogeneous mixture.
1. What is a Heterogeneous Mixture?
A mixture of sand mixed with salt is an example of a heterogeneous mixture. Heterogeneous mixtures possess different properties and compositions in various parts i.e. the properties are not uniform throughout the mixture.
Examples of Heterogeneous mixtures – air, oil, water, etc.
2. What is a Homogeneous Mixture?
Sugar mixed with water is the most common example of a homogeneous mixture. Homogeneous mixtures can be defined as the mixtures which possess the same properties and combination throughout their mass.
Examples of Homogeneous mixtures – alloys, salt, and water, alcohol in water, etc
Examples of Mixture
Crude oil: A mixture of organic compounds (mainly hydrocarbons)
Seawater: A mixture of various salt and water.
Air: a mixture of various gases like oxygen, carbon dioxide, nitrogen, argon, neon, etc.
Ink: A mixture of coloured dyes.
Gunpowder: A mixture of sulfur, potassium nitrate and carbon
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