Lesson 3

What are chemical bonds?

- Chemical bonds create big pieces of matter that we can see and interact with on our scale of reality - The force that sticks atoms together

Describe the basic physical characteristics of the following elements, and list their chemical symbols: carbon, chlorine, gold, hydrogen, oxygen, and sodium.

- Au (Gold): Gold atoms are quite massive, they are yellowish-metallic in color, and they lose their electrons easily - C (Carbon): Carbon atoms are moderately massive, they are black in color, and they lose electrons fairly easily - H (Hydrogen): Gas - O (Oxygen): Gas but can be cooled (weak van der waals forces bonds) - Na (Sodium): Soft metal; pure sodium is extremely reactive

Be able to recognize and explain space-filling models and ball and stick models of molecules.

- Ball and stick model: a visual model of matter which represents atoms as spheres, and covalent bonds as sticks linking the atoms together. Weak bonds may be represented by various other sorts of sticks or lines. - Space-filling model: a visual model of matter which represents atoms as spheres, and covalent bonds as atoms being smooshed together. Weak bonds may be represented by various sorts of lines.

What is the difference between the molecules in a compound, and the molecules in an element? For example, what is different between the molecules in water (a compound), and the molecules in oxygen (an element)?

- Compound: a type of matter composed of molecules that contain two or more different elements (think of water or glucose). If the molecules in a substance are composed of only ONE type of element, the substance - Element: : one of 118 fundamentally different kinds of atoms, such as carbon, chlorine, gold, hydrogen, oxygen, and sodium - For example, water contains two different elements - hydrogen and oxygen - making it a compound. Oxygen alone, however, contains two elements, but the same kind - two oxygens.

Where are electrons found in an atom, how fast are they moving, and what relationship do they have to the outer surface of an atom?

- Found in the outer surface - Moving 1000 miles per second - They form a haze cloud around the atom, thus they are the outer surfaces of all matter

Know that water, glucose and sodium chloride are compounds, be able to describe what atoms make them up, and in what amounts.

- Glucose contains atoms of hydrogen, carbon, and oxygen are held together with 'magical' covalent bonds. It is an entirely different substance that what makes them up. - Water is made up by one one oxygen and two hydrogens (H20) held by hydrogen bonds

Compare the types, patterns, and strengths of bonds in graphene, graphite, and diamond, and discuss how this relates to the strength of each substance.

- Graphene: An individual sheet of carbon atoms covalently bonded together; molecules - Graphite: Composed entirely of Carbon atoms; Weak bonds (Van Der Waals Forces) but contain some covalent bonds; not considered molecules - Diamond: Diamond is the second-strongest substance known, after graphene; entirely composed of carbon atoms just like a chunk of graphite

How do the bonds among atoms/molecules differ in the solid, liquid, and gaseous phases of matter?

- In a solid, atoms/molecules are tight - In a liquid, atoms/molecules are loose but not all over the place - In a gas, atoms/molecules are free to move wherever

Why can't you write a chemical formula for molecules that have no defined size?

- Molecules that have no defined size cannot be described with a chemical formula. Consider a water molecule. It has a defined size. It is always composed of two hydrogen atoms and one oxygen atom. Thus, we can write a chemical formula for it. - Both graphene and diamond are molecules. However, neither of them have a defined size. A sheet of graphene could contain six carbon atoms, or six trillion carbon atoms. The same is true for diamond. What would the chemical formula be? Certainly, you'd use C for carbon, but what would the subscript be? It could be any number, because the molecule can be any size. A chemical formula doesn't make sense for graphene or diamond, because their molecules have no defined size.

What are two major categories of chemical bonds, and how do they differ?

- Some bonds are created when atoms share their electrons with one another. - Other bonds occur after atoms steal electrons from neighboring atoms, or have their electrons stolen - COVALENT BONDS are the strongest bonds possible among atoms

Know, and be able to explain, the chemical formula for a molecule of water, a molecule of glucose, and a molecule of sodium chloride.

- Water: H20 - Glucose: C6H12O6 - Sodium Chloride: NaCl - Not all molecules have a chemical formula, like diamond, because it has no definite size.

What happens to the physical properties of individual atoms when they are held together with covalent bonds, and why does this seem strange?

- When atoms are bound together with covalent bonds, the physical properties of those atoms often disappear, and are replaced with new physical properties - A molecule is an item composed of two or more atoms, held together with covalent bonds

What is the nucleus of an atom, and where is it located?

A dense, central lump of particles and located in the center

What is the difference between a molecule and an atom?

Atoms are single neutral particles. Molecules are neutral particles made of two or more atoms bonded together. \

What is the difference between a compound and an element?

Compound refers to a molecule composed of two or more different elements. An element is simply a pure substance made up of 1 kind of atom.

How are atoms of different elements represented visually?

Each one has its own name, and a capitalized, one- or two-letter abbreviation, called a CHEMICAL SYMBOL

Which subatomic particles are responsible for chemical bonds?

Electron

What weak bonds hold water molecules together in the liquid and solid phases of water, and how do the bonds differ in each of these states?

Hydrogen Bonds

What happens to the properties of the atoms in a molecule, if you break the covalent bonds that are holding them together?

If you break all of the covalent bonds in a molecule, the atoms are liberated, and they regain their original properties. The properties of atoms are not 'lost forever' when they are bound into molecules. If the bonds are broken, the original properties of the atoms magically return.

What relationship do atoms have to all matter?

Matter is anything that has mass and atoms make up the mass

Are molecules always tiny?

No if covalently bonded, they can be big.

Are elements always composed of molecules?

No, the atoms in a molecule may be from the same element, or from different elements. Some elements, such as oxygen, are composed of molecules. Other elements, such as gold, are not composed of molecules. All compounds are composed of molecules

Can you tell whether a substance is a compound or an element, simply by looking at it?

No. Scientists have to conduct various types of chemical analyses In order to discover what atoms a substance is made of, and how those atoms are bound together

What is an element, and how many different ones are there?

One of 118 different kinds of atoms are called ELEMENTS

What are the two kinds of charge, and which kind do electrons have?

Positive and Negative Protons (+), Electrons (-)

What two subatomic particles are located in the nucleus of an atom, and which type has a positive charge?

Proton (+) and Neutron (no charge)

Why is a nugget of gold malleable?

The covalent bonds holding the gold nugget are weak.

How large is the nucleus of an atom, compared with the shell of electrons that surrounds it?

The nucleus of an atom is very tiny (almost invisible)

How, and why, does heat/temperature influence whether a substance is in a solid, liquid, or gaseous phase?

They speed up or slow down the movements of the atoms, causing them to change its physical properties.

Explain why compounds have different physical properties from the atoms that make them up.

When atoms are held together with covalent bonds, or when the pattern of covalent bonding among atoms changes, the physical properties of the individual atoms often disappear, and a new substance with different physical properties is created

What relationship do electrons have to electricity?

When charged particles move, they release energy

Is a drop of water composed of molecules? How about a bucket of water, or an ocean? Why or why not?

Yes because it contains two different elements - oxygen and hydrogen.

Are compounds always composed of molecules?

Yes, compounds are a type of matter composed of molecules that contain two or more different elements (think of water or glucose). If the molecules in a substance are composed of only ONE type of element, the substance

Is glucose composed of molecules? Why or why not?

Yes, it contains different elements