Lesson 4

Aloha! Ni Hao! Hola! Bonjour! Hello!

So this entry is gonna be about the lesson 4: pure substances and mixtures
Before starting with the actual topic, I shall explain some concepts to you, so let's begin.

• Atom: are the smallest unit of an element that maintains the properties of that element. Is like a building block of matter.
• Element: is made up of one or more of the same kind of atom chemically combined.
• Compound: a compund is made up of different kinds of atoms chemically combined. Compounds have different properties from the elements that make them up.
• Mixture: a mixture contains a variety of elements and compound that are not chemically combined with each other.

Elements and compounds are pure substances. Pure substance is asubstance that has definite physical and chemical properties such as appearence, melting point and reactivity. 

Physical changes do not change the identity of the substance. The chemical bonds that hold atoms together cannot be broken easily. To break or form chemical bonds, a chemical change is required.

When a pure substance undergoes a chemical change, it is no longer the same substance. line-height: By knowing the category to which an element belongs, ypu can predict some of its properties

font-family: Times, 'Times New Roman', serif;">Element are broadly classified as metals, nonmetals or metalloids. There are over 100 elements known to exist and each one has a place in the periodic table of elements. 

Compounds are grouped into basic categories by their properties. 

By their pH: They can be classified as acidic, basic or neutral by measuring their pH. Acids have a pH below 7. Bases on the other hand have pH values greater than 7 and neutral compounds have a pH of 7. 

Organic or Inorganic: In chemistry the word organic refers to compounds that contain carbon and hydrogen. Organic compounds are found in most foods. For example, gasoline contains a numer of organic ompounds, such as octane and heptane.

By their role in the body: Organic compounds that are made by living things are called biochemicals. They are divided into four categories: lipids, proteins, carbohydrates and nucleic acids.   Carbohydrates are a source of energy. Lipids store excess energy. Proteins build and repair body structures and Nucleic acids contain genetic information (DNA).