Atoms and elements - Science - Junior Secondary School

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Your Awesome Study Notes: Atoms and Elements

Hey there! Ready to dive into the super interesting world of atoms and elements? Ever wonder what you, your desk, the air, and even the stars are made of? The answer is tiny, tiny particles! In these notes, we'll explore these amazing building blocks of our universe. It might sound complex, but we'll break it down into simple, easy-to-understand parts. Let's get started on our adventure to discover what makes up everything around us!

1. The Tiniest Building Blocks: What is Everything Made Of?

Atoms and Elements: The LEGOs of the Universe

Imagine you have a giant box of LEGOs. You have red bricks, blue bricks, and yellow bricks. You can build anything with them - a car, a house, a spaceship!

In science, the universe is like a giant LEGO creation. The individual bricks are called atoms. They are the smallest, most basic building blocks of everything. An element is a substance that is made up of only ONE type of atom.

Example: A piece of pure gold is an element because it's made only of gold atoms.
Example: The oxygen we breathe is an element made only of oxygen atoms.

Common Elements and Their Symbols

Scientists are busy people, so they use shortcuts! Each element has a unique one or two-letter symbol. Here are a few you should know:

Hydrogen: H
Oxygen: O
Carbon: C
Iron: Fe
Copper: Cu
Gold: Au

Inside an Atom: Meet the Team!

Even though atoms are tiny, they are made of even smaller parts called subatomic particles. Think of an atom like a mini solar system.

In the centre (the nucleus):

Protons (p+): These have a Positive charge.
Neutrons (n⁰): These are Neutral (they have no charge).

Orbiting the nucleus:

Electrons (e⁻): These have a Negative charge and they zoom around the nucleus.

Memory Trick: Think P for Positive Proton and N for Neutral Neutron!

Normally, an atom has the same number of protons and electrons. This makes the atom electrically neutral because the positive and negative charges cancel each other out!

An Atom's ID Card: Atomic Number & Mass Number

Every element is unique, just like you! We can identify an element using two special numbers.

Atomic Number: This is the number of protons in an atom. It's the most important number because it defines what element it is. No two elements have the same atomic number. For example, any atom with 6 protons is ALWAYS a carbon atom.

Mass Number: This is the total number of protons AND neutrons in the nucleus. It tells us the mass of the atom (since electrons are so light, we don't count them in the mass number).

Did you know?

Atoms are incredibly small. You could fit about 100 million atoms side-by-side on a line just 1 cm long! And almost all of an atom's mass is packed into its tiny nucleus. The rest is just empty space!

When Atoms Get a Charge: Ions

What happens if an atom loses or gains an electron? It's no longer neutral! An atom that has an electrical charge is called an ion.

If an atom loses one or more electrons, it has more protons (+) than electrons (-), so it becomes a positively charged ion.
If an atom gains one or more electrons, it has more electrons (-) than protons (+), so it becomes a negatively charged ion.

This is important because ions are what allow elements to join together to make new things!

Key Takeaway for Section 1

Everything is made of atoms. An element is a substance with only one type of atom. Atoms are made of positive protons, neutral neutrons, and negative electrons. The number of protons (atomic number) tells you which element it is.

2. Organizing the Elements: The Periodic Table

A Super-Organized Chart for All the Elements

Scientists have discovered over 100 elements! To keep them all organized, they created a special chart called the Periodic Table. It looks complicated, but it's just a big grid that arranges elements in a very smart way.

The modern Periodic Table arranges elements in order of their atomic number (the number of protons), starting from 1 (Hydrogen) and going up.

Families of Elements: Groups

The vertical columns in the Periodic Table are called groups. Think of them as families. Elements in the same group have similar chemical properties, which means they behave in similar ways during chemical reactions.

For example, Lithium (Li), Sodium (Na), and Potassium (K) are all in Group 1. They are all soft, shiny metals that react very strongly with water. They're like reactive cousins!

Metals, Non-Metals, and the In-Betweens

The Periodic Table has a thick "staircase" line that divides the elements into three main types based on their physical properties.

Metals (on the left side): These are usually shiny, strong, and great at conducting heat and electricity. Think of iron, copper, and gold.

Non-Metals (on the right side): These are often dull, brittle (if they are solid), and are poor conductors. Many are gases at room temperature. Think of oxygen, carbon, and sulphur.

Semi-metals (along the staircase): These have properties that are a mix of both metals and non-metals. They are very useful in electronics! Silicon is a famous example.

Key Takeaway for Section 2

The Periodic Table organizes elements by their atomic number. Elements in the same column (group) are like a family and have similar properties. Elements can be classified as metals, non-metals, or semi-metals.

3. Mixing and Joining: Compounds and Mixtures

Now that we know about elements, let's see what happens when they get together. Don't worry, this is easier than it sounds!

Just Hanging Out: What is a Mixture?

A mixture is when two or more substances are mixed together, but they are NOT chemically joined. The cool thing about mixtures is that you can usually separate them back into their original parts.

Analogy: A salad is a mixture. You mix lettuce, tomatoes, and cucumbers. You can still see each vegetable, and if you really wanted to, you could pick them all out again. Other examples include air (a mixture of gases like oxygen and nitrogen) and salt water.

Sticking Together: What is a Compound?

A compound is formed when atoms from two or more different elements join together through a chemical change (or chemical reaction). This forms a completely new substance with its own unique properties.

Analogy: Baking a cake is like making a compound. You mix flour, sugar, and eggs (elements), but after baking (a chemical reaction), you get a cake! You can't un-bake the cake to get the flour and sugar back. The cake is a totally new thing.

A famous example of a compound is water (H₂O). It's made from two hydrogen atoms chemically joined to one oxygen atom. Hydrogen and oxygen are both gases, but when they form a compound, they make a liquid - water!

Quick Review: Element vs. Compound vs. Mixture

Element: One type of atom. (e.g., Iron, Fe)
Compound: Different atoms chemically joined. (e.g., Water, H₂O)
Mixture: Different substances physically mixed, not joined. (e.g., Air)

Key Takeaway for Section 3

Mixtures are substances that are just mixed together and can be separated. Compounds are new substances formed when elements chemically join together. Creating a compound is a chemical change.

4. The World of Materials

Humans are clever! We've learned to take elements and compounds and turn them into all the useful materials we use every day.

Amazing Metals

Metals are super useful! Most metals are not found in their pure form in nature. They are usually found as compounds in rocks called ores. Getting the metal out of the ore is called extraction.

Did you know? The "Bronze Age" and "Iron Age" are named after metals! Copper and tin (which make bronze) are easier to extract than iron. So, humans learned to use bronze first. Later, when they developed better technology, they could extract iron, which is stronger, and the Iron Age began!

We use metals for everything from buildings and bridges (because they are strong) to electrical wires (because they are good conductors).

Better Together: Alloys

An alloy is a material made by mixing a metal with other elements (often other metals) to give it better properties. It's like creating a super-metal!

Example: Pure iron rusts easily and isn't super strong. But if you mix it with a little bit of carbon, you get steel, which is much stronger and is used to build skyscrapers!
Example: Many coins are made of alloys like bronze or cupronickel to make them last longer.

From Black Goo to Everything: Crude Oil & Plastics

Crude oil is a thick, black liquid found deep underground. It's a mixture of many different substances called hydrocarbons. We can separate these useful substances using a process called fractional distillation.

Some of the separated parts are used for:

Fuels like petrol for cars.
Solvents for things like paint.
Making plastics!

Plastics are amazing materials made from crude oil. They are lightweight, strong, and can be moulded into any shape. Look around you – your pen, your phone case, your water bottle – they are probably made of plastic!

The Problem with Our Stuff: Environmental Issues

While metals and plastics are incredibly useful, they also cause problems for our planet.

Pollution: Making and using these materials can pollute the air and water.
Waste: Many plastics don't break down naturally. They end up in landfills or in our oceans for hundreds of years, harming wildlife.

What can we do? The best solution is to follow the 3 R's: Reduce, Reuse, and Recycle! By recycling metals and plastics, we can save resources and protect our environment.

Key Takeaway for Section 4

We get useful materials like metals and plastics from nature. Alloys are mixtures that improve a metal's properties. While these materials are useful, we must be careful to reduce waste and recycle to protect our environment.