Chemical Compounds Review

Review of Metallic Bonding When you look at a piece of metal (i.e. a gold ring), the metal atoms are clearly sticking together pretty strongly (the ring doesn’t evaporate or crumble to pieces, right?) This sticking occurs because the atoms are sharing electrons. This sharing is different from the sharing in a covalent bond. In a covalent bond only two atoms are sharing a single pair of electrons, whereas metal atoms share electrons freely with all of the atoms around them. We call this the “sea of electrons model”. A good analogy is that a covalent bond is like a typical family – two parents bonded by a couple of shared kids. Molecules are like modern families – small, independent units! Metallic bonding is more like a giant hippie commune where lots of parents are bound together and share lots of kids – one big community rather than a single unit. This is why metals are flexible and malleable – the atoms are not bound into rigid structures – they can remain firmly bonded while the angles between them are changed.

The “Sea of Electrons” Cu

Examples of metals: monex.com mountainsteps.blogspot.com stockwatch.in

Review of Ionic Bonding Atoms are most stable when they have a full outer shell of electrons. They can achieve this by either losing electrons (and becoming positive ions) or gaining electrons (and becoming negative ions). Ex – Unstable Na loses an electron and becomes stable Na +. Unstable Cl gains an electron and becomes stable Cl -. Oppositely charged ions attract each other and stick together to form ionic compounds. So Na+ and Cl - get together to form the compound NaCl. Ionic bonds form between atoms with LARGE electronegativity differences.

Review of Ionic Compounds Ionic compounds are not single units, they are large crystals made up of trillions of atoms. The ratio of the types of atoms found is constant and shown in the formula. – For example, an MgCl 2 crystal has one Mg atom for every two Cl atoms. The bonds between the atoms are rigid – this is why salt doesn’t bend like metal! A common name for many ionic compounds is “salts”. Salts that dissolve in water (and conduct electricity) are called “electrolytes”. Most ionic compounds are solid crystals at room temperature.

Examples of Ionic Compounds reallynatural.com Table Salt: NaCl homesteadrevival.blogspot.com Epsom Salt: MgSO 4 chem1.com Copper Sulfate, CuSO 4 yinhejituan.com Potassium chromate, KCr 2 O 4 liboxgoa.com Potassium Permanganate, KMnO 4

Review of Covalent Bonding If two atoms have similar electronegativities, they will obtain full outer shells by sharing electrons. These shared electrons are called a “covalent bond”. Covalent bonds form between nonmetals, i.e. hydrogen and oxygen combine to form H 2 O.

Review of Covalent Compounds Uncharged covalent compounds are called molecules. Molecules are separate entities rather than large networks of atoms. This means that molecular substances tend to be gases at room temperature – the individual molecules don’t stick together much. Water is an exception because it is polar – the small electrical charges on a water molecule cause the molecules to hold together enough to form a liquid. Another exception is sugar – C 6 H 12 O 6 - sugar molecules stick to each other to form large crystals. Water moleculesNaCl crystal Sodium Ion

Examples of Covalent Compounds scienceblogs.com Water, H 2 O pacificwestmarketing.com Oxygen, O 2 dust-control-inc.com Methane, CH 4 (burning) chemicalformula.org Ammonia, NH 3 Ethyl Alcohol, CH 3 CH 2 OH

Compounds Matter is not typically made up of individual atoms. Rather, it is made of atoms that are bound together into larger units. A group of atoms bound together is called a ____________. Atoms that have opposite electrical charges are called __________ and stick together to form ____________ bonds and compounds. Atoms that have similar electronegativities form bonds by _____________ electrons. These are called ____________ bonds/compounds. An uncharged group of covalently bound atoms (i.e. H 2 O) is called a _____________. Uncharged metal atoms also stick together in networks of atoms that freely share electrons. We call this ___________bonding and the model the ___________ of electrons model.

To Review: All matter is made of ______. There are different kinds of atoms. Atoms can range from tiny hydrogen atoms (1 proton, 1 electron) to huge gold atoms (79 protons) and Uranium atoms (92 protons). We call the different types of atoms “_________”. Not all atoms of an element are identical. They all have the same number of __________ but can have different numbers of __________ and __________. Atoms of the same element that have different masses (due to different numbers of neutrons) are called __________. Atoms of the same element that have electrical charges (due to different numbers of electrons) are called ___________. Since atoms are so tiny, we use a very large number to count them. This large number used to count atoms is called a ________. A mole of atoms is equal to _______________ atoms. Since we can’t count atoms, we collect the right number of them in the lab by _______________ the element. Where do we find the mass of one mole of atoms of an element?