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Welcome! Today we will explore how scientists discovered the secret parts of the atom over time.
Long ago, John Dalton said atoms were like solid billiard balls. Later, J.J. Thomson discovered tiny negative electrons stuck inside a positive sphere, like chocolate chips in cookie dough.
Ernest Rutherford showed that atoms are mostly empty space. He proved that positive protons are packed into a tiny center called the nucleus, while electrons orbit around it.
Niels Bohr improved this by showing electrons travel in set paths called energy levels. Today, the quantum model shows electrons buzzing in a cloud, rather than neat tracks.
We can model matter to classify it. Elements have one kind of atom, while compounds have different atoms bonded together. Mixtures just mix things without bonding.
Classify a molecule of water (H2O) and identify its atoms using your knowledge of atomic theory and the periodic table.
- Step 1: Look at the chemical formula, H2O. Identify the element symbols: 'H' stands for Hydrogen and 'O' stands for Oxygen.
- Step 2: Use the periodic table to find these elements. Hydrogen (H) is atomic number 1, and Oxygen (O) is atomic number 8.
- Step 3: Count the atoms. The subscript 2 means there are two Hydrogen atoms. No subscript on 'O' means there is one Oxygen atom.
- Step 4: Determine if they are bonded. Because they are chemically combined in a set ratio, this is a compound, not just a mixture.
- Step 5: Conclude that H2O is a compound made of two different elements (Hydrogen and Oxygen) bonded together.