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Elements and Compounds  – Grade 7 Science Worksheets

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Elements

Everything around us is made up of elements. Let’s take the air we breathe is mixture so many elements like oxygen, nitrogen, and argon. They are the constituting factors for everything on this planet Earth: the tree, your book, your pencil, paper, and furniture, so on.

An element is a pure substance that cannot be broken down by chemical methods into simpler parts.

 

For example,

  • A piece of iron cannot be broken down into anything other than iron. If you kept breaking that piece,  the pieces would get smaller, but each piece will always be iron.

Elements, compounds, physical and chemical changes

Credit: https://www.pexels.com/photo/carpentry-close-up-nails-sharp-190101/

  • A copper wire is an example of an element/ pure substance. The more we break it down, more pieces of copper we get.

Elements, compounds, physical and chemical changes

Credit: https://pixabay.com/en/copper-or-sun-wire-sky-1711056/

Elements, compounds, physical and chemical changes

 

Elements consist of only one type of atom. An atom is the smallest particle of an element that still has the same properties of that element. All atoms of a specific element have exactly the same chemical makeup, size, and mass.

 

 

There are a total of 118 elements.

Many elements occur naturally on Earth; however, some are created in a laboratory by scientists by nuclear processes.

 

Compounds

Every combination of atoms is a molecule. Numerous atoms of different elements combine to form a compound molecule. All compounds are molecules but all molecules are not compounds. Molecule is one that is formed together out of a chemical bond.

 

For example:Elements, compounds, physical and chemical changes

  • Sodium (Na) is a molecule, but not a compound because it is made of only one element.
  • Common Salt (NaCl) can be called a molecule or a compound because it is made of Sodium Na, and Chlorine Cl.
  • One atom of carbon + one molecule of oxygen = one molecule of carbon dioxide.

Elements, compounds, physical and chemical changes

An illustration of how element compound and mixture looks like:

Elements, compounds, physical and chemical changes

Credit: https://chemistry.stackexchange.com/questions/2879/what-is-the-definition-of-of-compound-mixture-element-and-molecule

elements

 

What elements and compounds have in common?

Both, elements and compound are pure chemical substances.

Physical changes: A change which does not affect the substance. Physical forces cannot always break down compounds totally. Heat melts ice to form water. But no change happens to the molecule of water. Like -wise decreasing the pressure boils water leaving the molecules unchanged.

Elements, compounds, physical and chemical changes

Chemical changes in compounds happen when chemical bonds are created or destroyed.

In a chemical change the forces between atoms, changes the molecular pattern of a substance. Energy is either released or absorbed in the process.

The process of curdling of milk is also an example of chemical change.

  1. A new substance is formed.
  2. The process is irreversible.

 

There are millions of different compounds around us. When elements join and become compounds, they lose many of their individual behavior. Sodium (Na) is very reactive element individually but when sodium and chlorine (Cl) combine, table salt forms which is a non-reactive and obviously very edible substance. New compounds formed rarely posses any of their previous physical or chemical traits when they were elements. They have a new life of their own.

Check Point

 

A. Fill in the blanks:

  1. An ………………. Is a pure substance that cannot be broken down by chemical methods into simpler components.
  2. An …………..is the smallest particle of an element that still has the same properties of that element.
  3. There are a total of ………. elements.
  4. A …………… is a molecule made of atoms from different elements.
  5. …………………. ……………….in compounds happen when chemical bonds are created or destroyed.

 

B. State True or False:Elements, compounds, physical and chemical changes

  1. All atoms of a specific element have the different chemical makeup, size, and mass.
  2. Molecule is used to describe any atoms that are together by a chemical bond.
  3. Every compound is a molecule, and every molecule is a compound.
  4. When elements join and become compounds, they do not lose many of their individual behaviors.
  5. Physical forces alone rarely break down compounds completely.
Answer Key
A. Fill in the blanks:

  1. Element
  2. Atom
  3. 118
  4. Compound
  5. Chemical Changes

 

B. State True or False

  1. False
  2. True
  3. False
  4. False
  5. True

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