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Welcome! Today we will explore how scientists discovered the structure of the atom, from solid spheres to quantum clouds.
Matter is anything that has mass and takes up space. We can classify matter as pure elements, compounds, or different types of mixtures.
John Dalton imagined atoms as solid, indivisible spheres. Later, J.J. Thomson discovered negative electrons scattered inside a positive sphere, like chocolate chips in cookie dough.
Ernest Rutherford proved atoms are mostly empty space with a tiny, positive nucleus. Niels Bohr then showed electrons orbiting the nucleus in fixed, circular energy levels.
Today, the quantum mechanical model describes electrons not in neat tracks, but buzzing inside fuzzy, 3D probability clouds called orbitals.
Classify a glass of clean tap water containing dissolved oxygen gas, and identify the atoms involved using your periodic table.
- Analyze the substances present: we have liquid water (H2O) and dissolved oxygen gas (O2).
- Determine if it is a pure substance or a mixture. Because there are two different molecules mixed together uniformly, it is a homogeneous mixture.
- Use the periodic table to identify the atoms. 'H' stands for Hydrogen (atomic number 1) and 'O' stands for Oxygen (atomic number 8).
- Conclude that the mixture contains hydrogen and oxygen atoms chemically bonded into water molecules, alongside free oxygen molecules.