Grade 1
  1. Numbers and Counting  1.1. Counting to 10  1.2. Counting to 20  1.3. Counting to 50  1.4. Counting to 100  1.5. Writing Numbers 1 to 10  1.6. Writing Numbers 1 to 20  1.7. Writing Numbers 1 to 50  1.8. Writing Numbers 1 to 100  1.9. Reading Numbers 1 to 10  1.10. Reading Numbers 1 to 20  1.11. Reading Numbers 1 to 50  1.12. Reading Numbers 1 to 100  1.13. Comparing Numbers  1.14. Ordering Numbers  1.15. Odd and Even Numbers  1.16. Number Patterns  1.17. Skip Counting by 2s, 5s, and 10s  1.18. Understanding Zero
  2. Basic Addition and Subtraction  2.1. Understanding Addition  2.2. Addition Facts within 10  2.3. Addition Facts within 20  2.4. Adding Zero  2.5. Adding One More  2.6. Adding Two More  2.7. Adding Three More  2.8. Adding Using Pictures  2.9. Addition Word Problems  2.10. Understanding Subtraction  2.11. Subtraction Facts within 10  2.12. Subtraction Facts within 20  2.13. Subtracting Zero  2.14. Subtracting One  2.15. Subtracting Two  2.16. Subtraction Using Pictures  2.17. Subtraction Word Problems  2.18. Introduction to Doubles Facts  2.19. Introduction to Making 10
  3. Place Value and Number Sense  3.1. Understanding Tens and Ones  3.2. Counting by Tens  3.3. Place Value within 20  3.4. Place Value within 50  3.5. Place Value within 100  3.6. Reading and Writing Two-Digit Numbers  3.7. Comparing Two-Digit Numbers  3.8. Decomposing Numbers
  4. Measurement  4.1. Length  4.1.1. Comparing Lengths  4.1.2. Measuring with Non-Standard Units  4.1.3. Using Standard Units (Inches and Centimeters) in Length  4.2. Weight  4.2.1. Comparing Weights  4.2.2. Heavy and Light Objects  4.2.3. Introduction to Grams and Pounds  4.3. Capacity  4.3.1. Comparing Capacity  4.3.2. Full and Empty  4.3.3. Introduction to Liters and Milliliters  4.4. Time  4.4.1. Telling Time to the Hour  4.4.2. Telling Time to the Half Hour  4.4.3. Days of the Week  4.4.4. Months of the Year  4.4.5. Understanding Yesterday, Today, and Tomorrow  4.5. Money  4.5.1. Recognizing Coins  4.5.2. Counting Coins  4.5.3. Introduction to Dollar and Cents Symbols  4.5.4. Simple Addition and Subtraction with Money
  5. Geometry  5.1. 2D Shapes  5.1.1. Recognizing 2D Shapes  5.1.2. Drawing 2D Shapes  5.1.3. Naming 2D Shapes  5.1.4. Properties of 2D Shapes  5.1.5. Sorting 2D Shapes  5.1.6. Composing Simple Shapes  5.2. 3D Shapes  5.2.1. Recognizing 3D Shapes  5.2.2. Naming 3D Shapes  5.2.3. Properties of 3D Shapes  5.2.4. Sorting 3D Shapes  5.3. Position and Direction  5.3.1. Left and Right  5.3.2. Above and Below  5.3.3. Inside and Outside  5.3.4. Near and Far  5.3.5. In Front and Behind
  6. Patterns and Sorting  6.1. Recognizing Patterns  6.2. Extending Patterns  6.3. Creating Patterns  6.4. Sorting by Color  6.5. Sorting by Shape  6.6. Sorting by Size
  7. Data and Graphing  7.1. Introduction to Data  7.2. Collecting Data  7.3. Tally Marks  7.4. Bar Graphs  7.5. Picture Graphs  7.6. Interpreting Simple Graphs
  8. Fractions  8.1. Understanding Halves  8.2. Understanding Fourths  8.3. Dividing Shapes into Equal Parts  8.4. Identifying Equal and Unequal Parts

Grade 1 → Geometry → 2D Shapes ↓


Properties of 2D Shapes


In geometry, 2D shapes are flat figures that have only two dimensions: length and width. They do not have depth or thickness like 3D shapes. It is very important to understand the properties of these shapes because they are all around us and we use them often in our daily lives.

Basic properties of 2D shapes

When we talk about 2D shapes, there are several basic properties we often discuss. These include:

  • Sides: Straight or curved lines that form the boundaries of the shape.
  • Vertices (corners): The points where two sides of a shape meet.
  • Edges: The length along the border of the shape.

Common 2D shapes and their properties

Circle

A circle is a 2D shape that is perfectly round. It is different from other shapes because it does not have straight lines or corners.

  • Sides: 0 – It has a continuous curved line.
  • top: 0 - no corners.
  • Radius: The line segment from the center of a circle to any point on its boundary.

A real example of a circle is pizza. Even though it is cut into slices (triangles), the entire pizza is one large circle.

Square

A square is a 2D shape with four equal sides and four corners. All the angles of a square are right angles, which means each of them is 90 degrees.

  • Sides: 4 – All sides are of equal length.
  • Vertex: 4 – It has four corners.
  • Angle: 90 degrees each.

Think of a slice of cheese or the surface of a chessboard. These are all familiar square shapes.

Rectangle

A rectangle is similar to a square, but its sides have different lengths. It has four sides like a square, but the opposite sides are equal.

  • Sides: 4 – Opposite sides are of equal length.
  • Vertex: 4 – It has four corners.
  • Angle: 90 degrees each.

The shape of a book or computer screen is usually rectangular. This is a very common shape in our everyday life.

Triangle

A triangle is a shape with three sides and three corners. Its sides can be of equal length or of different lengths.

  • Sides: 3
  • Zenith: 3
  • Types: Equilateral (all sides equal), Isosceles (two sides equal), Scalene (no sides equal).

If you look at any mountain, you will find that its peak forms a triangular shape with its base.

Pentagon

A pentagon is a two-dimensional shape with five sides and five corners.

  • Sides: 5
  • Zenith: 5

The famous building for the Department of Defense in the United States is called “Pentagon” and its shape is like a pentagon.

Calculating perimeter and area

It is very important to understand how to calculate the perimeter and area of these shapes. The formulas can help us measure their size and understand more about them.

Circumference

The perimeter is the distance around the shape. To find the perimeter you add the lengths of all its sides together.

  • Circle: The perimeter is called the circumference. It is calculated as follows:
    C = 2πr
  • Square:
    P = 4 × side
  • Rectangle:
    P = 2 × (length + width)
  • Triangle: Add all sides together:
    P = side1 + side2 + side3

Area

Area is the amount of space inside a shape. Imagine how much paint you would need to cover the surface of the shape. Here are some simple formulas:

  • Circle:
    A = πr²
  • Square:
    A = side × side
  • Rectangle:
    A = length × width
  • Triangle:
    A = ½ × base × height

Activities and sports

Learning about 2D shapes can be a lot of fun. There are many activities that can help you understand and remember the properties of these shapes. Here are some suggestions:

  • Shape Search: Search around your home or school to find examples of the shapes you discussed. Make a list of them as you find them.
  • Draw and decorate: Create different 2D shapes and try decorating them using colors or patterns.
  • Shape Matching: Use the cut out shapes and try to match the objects around you with those shapes.

Conclusion

Understanding the properties of 2D shapes is a basic skill in geometry that helps us understand the world around us. With clear understanding and practice, you will be able to identify these shapes, measure them, and use them in different contexts.


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Properties of 2D Shapes

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