# Naming 2D Shapes Using Sides and Corners

Naming 2D Shapes using Sides and Corners

# List of 2D Shape Names and their Properties

• 2D means 2-Dimensional. A 2D shape has two dimensions, which are length and width.
• A 2D shape is a shape that has no thickness. If drawn on paper, it would be completely flat.
• To name a 2D shape we simply count how many sides or corners it has.
• A side is a straight line in between two corners of a shape.
• A corner is where two sides meet.
• A shape is made when the sides form an enclosure.
• The length of all the sides added together is called the perimeter.
• The number of sides is the same as the number of corners.
We count the number of sides or corners.

The number of sides or corners tells us the name of our 2D shape.

• To name a 2D shape we count how many sides or corners it has and look at our list of 2D shapes.
• This shape has 5 straight sides.
• The number of corners is the same as the number of sides.
• This shape has 5 corners.
• From our 2D shapes list, the name of a shape with 5 sides or 5 corners is called a pentagon.

# Naming 2D Shapes Using Sides and Corners

To name a 2D shape we count the number of corners it has. An alternative way to name a 2D shape is to count the number of sides it has. When we have counted the number of sides or corners we can read the shape name from our list of 2D shapes below:

In this lesson we will go into more detail about 2D shapes and breakdown some of the more common shapes that we might see.

If a shape is 2D it means that it has 2 dimensions. When we say 2 dimensions we mean that one dimension is the shape’s length and the other dimension is the shape’s width.

A 2D shape is flat and can only be drawn on a piece of paper. It cannot exist in real life as it does not have a thickness, just a length and width.

Any physical object that we can hold is not a 2D shape, it is a

shape. The main difference between a 2D and a 3D shape is that a 3D shape has a depth, or thickness, whereas a 2D shape does not.

The two main properties of 2D shapes are sides and corners:

A side is a straight line on the edge of a 2D shape.

A corner is where two sides meet.

The perimeter property is the total distance around the edge of a 2D shape.

The number of sides or corners tell us the name of which 2D shape we have.

## Triangles have 3 sides and corners

Any 2D shape with three corners or three sides is called a triangle.

We look for three straight lines that enclose an area.

Any shape with 3 sides and 3 corners is called a triangle. A triangle is a 2D shape.

All angles in a triangle add up to 180

.

## Quadrilaterals have 4 sides and corners

The 2D shapes below all have four corners and four sides.

The correct name for any 2D shape with four sides is a quadrilateral.

A quadrilateral is just the word we use for a four-sided shape.

Two common types of quadrilaterals are squares and rectangles.

A square has four sides that are the same length.

When teaching 2D shape names to children, it is a very common misconception for them to say that the name of any four-sided shape is called a square.

The only correct name to call all types of four-sided shapes is ‘quadrilateral’. The name ‘square’ is only correct to use for a shape that has four equal sides, meaning that all of its sides are the same length.

A rectangle has two pairs of opposite sides that are the same length.

Each side is the same length as the side that it is opposite to.

A square is a special kind of rectangle that has all sides the same length.

Both shapes have four

.

## Pentagons have 5 sides and corners

Any shape with five corners or five sides is called a pentagon.

Pentagons are 2D shapes that have 5 corners and 5 sides such as any of the shapes in the image above. The shape in the middle of the image is a regular pentagon because it has 5 sides that are all the same length.

The name of the other shapes around the outside are irregular pentagons. Irregular means that they do not have all sides the same length.

## Hexagons have 6 sides and corners

Any 2D shape with six corners or six sides is called a hexagon.

Again the shape in the centre of this image is a regular hexagon because all of its six sides are equal.

The other 2D shapes around the outside are called irregular hexagons because they do not have six sides that are all the same length.

Remember that to decide if a shape is regular, we can only look at the sides and see if they are all the same length. We cannot decide if a shape is regular from the number of its corners. Although if its angles were all the same size, then we could see that it would be regular.

## Circles have no corners

The shape below is different to the previous 2D shapes that we have looked at as it is made from one curved side. It also does not have any corners.

This 2D shape is a circle.

A circle is the name we give to a 2D shape with one curved side and no corners.

For a shape to be a circle it must also look exactly the same when we rotate it around.

A circle does not have any straight sides.

Instead, we say that it has one continuous curved side.

When teaching 2D shapes, a circle is a common shape that children will encounter. Sometimes children will mistakenly call any shape that is made from a curved side a circle.

The 2D shape below is an ellipse. An ellipse is a 2D shape made from one curved side and no corners, however it has a different width compared to its height. It is not a circle because it is wider than it is tall.

Remember when naming 2D shapes, we use the number of sides or corners. However it is important to be familiar with the names and I recommend using our 2D shape names list above to help your child recognise the common shape names.

The final additions to our list of 2D shapes are heptagons and octagons.

A seven-sided shape is called heptagon.

An octagon is an eight-sided shape.

Most primary schools will teach 2D shapes up to octagons.

Now try our lesson on How to Find the Perimeter of Rectangles and Squares where we learn how to add the side lengths of a shape to work out the perimeter.

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