Metal ions sit in a regular lattice inside a sea of delocalised electrons. That one picture explains conduction, malleability, and why an alloy is harder than the pure metal.
Graphite handed you one useful idea: a delocalised electron, belonging to no particular bond and free to travel. In the covalent world that was the exception, and it took a special arrangement to get it. In a metal it is the rule. Every atom in the copper wire coming out of the cable crate has given up its outer electrons to the same shared pool, so the electrons belong to the whole piece rather than to any two atoms. That one difference explains almost everything a metal does.
A metal atom has as many outer electrons as its group number, so one, two or three, and it parts with them easily. In a lump of copper every atom does exactly that, and the electrons have nowhere to go, because there is no non-metal waiting to take them. So they pool. What is left behind is a regular lattice of positive ions sitting in a sea of delocalised electrons that runs through the whole piece. The metallic bond is the attraction between those positive ions and that sea, and it pulls in every direction at once.
Two things follow straight away. Electricity first: the delocalised electrons are already free to move, so pushing on them at one end sends charge through the metal. Unlike an ionic solid, a metal never has to melt first. Heat next: those same electrons carry energy as they travel, and they travel fast, so a metal spreads heat through itself far quicker than a plastic does. That is why a metal spoon in hot water warms along its length, and why a metal bench feels cold to touch. It is taking heat out of your hand.
Now push on it. The ions sit in layers, and every ion in a pure metal is identical, so a layer can slide one place over and everything still fits. The electron sea slides with it and the bond survives, which is why copper can be hammered flat or drawn into wire instead of shattering. That is what malleable means. An alloy spoils it on purpose. Mixing in atoms of a different size makes the layers uneven, so they no longer slide cleanly past each other. That is why bronze, which is copper with a little tin in it, is harder than copper.
Look along the bench. The copper in the cable is close to pure, because pure copper conducts best and bends without snapping. The phone's frame is an aluminium alloy, since pure aluminium is too soft to survive a pocket. The solder on the board is an alloy too, mixed so that a hot soldering iron can melt it without cooking the components beside it. The brass in the connector is copper with zinc in it. Every one of those is the same electron sea, with the ions arranged to suit a different job.
A metal is a lattice of positive ions sitting in a sea of delocalised electrons, and the bond is the pull between the two. Those free electrons carry both current and heat, and they do it in the solid, unlike an ionic compound. Identical ions let layers slide, so a pure metal bends rather than breaks. Mixing in a different-sized atom stops the sliding, which is what makes an alloy harder.
Graphite left the club with one idea worth keeping: an electron that belongs to no particular bond and can travel. The cable crate is full of copper wire, and every copper atom in it does the same thing.
Each copper atom lets its outer electrons go. Where do they end up?
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Nothing builds on it yet.
Jobs that lean on this skill. Follow one to see everything it is built on.
24 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.