Atomic Structure Basics

Ever wondered what makes gold different from oxygen? It's all about atomic structure and how particles are arranged. An element contains only one type of atom (like pure gold), whilst a compound has different types of atoms chemically stuck together (like water, H₂O).

Mixtures are completely different - they're just different substances mixed together without any chemical bonding happening. Think of it like a fruit salad where each piece of fruit keeps its own identity.

There's a handy naming trick for compounds: if there are only two elements, the name ends in 'ide' (like copper oxide). With three elements, it usually ends in 'ate' (like barium carbonate). The exception is compounds with 'OH' - these are always called hydroxides.

Quick Tip: Remember that protons and neutrons have roughly the same mass $relative mass = 1$, but electrons are tiny - about 2000 times lighter!

Inside the Atom

The numbers on the periodic table tell you everything about an atom's structure. The mass number (big number) equals protons plus neutrons, whilst the atomic number (small number) tells you how many protons are there.

Here's the key relationship: number of electrons always equals number of protons in neutral atoms. To find neutrons, simply subtract the atomic number from the mass number.

Isotopes are atoms of the same element with different numbers of neutrons - like two versions of the same person wearing different shoes. Chlorine has isotopes with either 18 or 20 neutrons, but both still have 17 protons.

Electron shells work like energy levels around the nucleus. Electrons fill up the closest shell first (maximum 2), then the second shell (maximum 8), and so on. The number of outer electrons matches the group number on the periodic table, whilst the number of shells matches the period number.

Remember: Noble gases have full outer shells, which is why they're so unreactive - they're already 'happy'!

Chemical Bonding

Atoms bond together because they want full outer shells like the noble gases. There are two main types: ionic bonding $between metals and non-metals$ and covalent bonding $between non-metals only$.

In ionic bonding, electrons transfer completely from metal to non-metal atoms. Metals lose electrons and become positive ions, whilst non-metals gain electrons and become negative ions. Think of sodium chloride: sodium gives up one electron to become Na⁺, and chlorine accepts it to become Cl⁻.

These oppositely charged ions attract each other through electrostatic forces, creating a giant lattice structure. This isn't just a few ions stuck together - it's a massive, regular pattern that continues in all directions throughout the entire crystal.

Scientific models help us visualise these complex structures in simpler ways, showing the key features without overwhelming detail.

Key Point: Metals always form positive ions, non-metals always form negative ions - opposites attract!

Properties of Ionic Compounds

Ionic compounds have distinctive properties that all stem from their giant lattice structure and the strong forces holding ions together. They have high melting points because you need loads of energy to break those strong electrostatic attractions between ions.

Water can dissolve many ionic compounds because the charged ions attract water molecules and form weak bonds with them. The ions basically get surrounded by water molecules and pulled away from the lattice.

Electrical conductivity depends on whether ions can move. In solid form, ionic compounds don't conduct electricity because ions are locked in fixed positions. However, when molten or dissolved, the ions become free to move and can carry electrical current between electrodes.

Ionic compounds are brittle - they shatter rather than bend. When you try to change their shape, you end up pushing ions with the same charge next to each other, and they repel strongly enough to break the structure apart.

Remember: Free-moving ions = electrical conduction. Fixed ions = no conduction.

Metallic Bonding and Properties

Metallic bonding creates a completely different structure called a giant metallic lattice. Picture positive metal ions surrounded by a 'sea' of delocalised electrons that are free to move throughout the entire structure.

These mobile electrons explain why metals are such good electrical and thermal conductors - the electrons can move freely and carry charge or energy. The strong metallic bonds also give metals high melting and boiling points.

Unlike ionic compounds, metals are malleable (can be hammered into shapes) and ductile (can be drawn into wires). This happens because layers of atoms can slide over each other whilst maintaining the metallic bonding - the electron sea just flows around the moving atoms.

Scientists use different models to represent these structures, from simple 'ball and stick' diagrams to more realistic 'space-filling' representations that show how tightly packed atoms really are.

Fun Fact: The same delocalised electrons that let metals conduct electricity also make them shiny - they reflect light really well!