In Sci

Concept Review Page – Test on Electrons, bonding

What is an atom?  What are the fundamental particles that make up the atom? What composes most of the mass of the atom? What occupies most of the space of the atom? What is the mass of a proton or a neutron and how does it compare to an electron’s mass? (see below)

What information can be found on the periodic table for each element? What is the atomic number? Can an element have two (on more?) different types or sizes of nuclei? Can they have different numbers of protons? Of neutrons? Of electrons?  What is atomic mass? What are isotopes?

What is a Bohr orbital (ring) model?  Why does the Bohr model not adequately capture the electron configuration of an element?  How is a p-orbital shape different from a “Bohr orbit” ring idea? Where are the s, p, d, and f blocks on the periodic table?  What is the filling order for the sublevels, and how many electrons can each one hold?

What patterns or trends in atomic properties can be seen on the periodic table? What do the elements in columns 1 & 2 have in common? What about columns 16 (6A) & 17 (7A)? What is special about the elements in the last column (VIII-A) on the periodic table? What are they called?

What are the differences between ionic and covalent bonds? How is an ionic bond formed? What are some examples of ionic compounds? How does the formula of an ionic compound indicate the ratio of ions in the substance? What is NaCl? In what ratio would you expect calcium to combine with chlorine to form an ionic compound? What about Scandium and sulfur ? How do you name these compounds?  

How are the electrons distributed around the atoms in a covalently bonded molecule? What forces cause atoms to enter into covalent bonds in which their electrons are shared with another atom?  What determines how many bonds an atom (like C, N, O, or H) is likely to form? What is the octet rule? What are Lewis structures? How do molecular models reflect the bonding tendencies of atoms?  How are molecular models different from real atoms?  What is a Lewis Dot structure?

Atom

Nucleus

Proton

Neutron

Electron

Rutherford Gold Foil experiment

Alpha particle

Element

Atomic number

Atomic mass

Isotope

Isotopic mass

Energy level

Bohr orbit

Electron configuration

Valence shell

Ion

Ionic Bond

Covalent Bond

Cation / anion

Molecule

Compound

Lewis Structure

Octet / Octet Rule

Just to clarify, there will  be a Periodic Table provided with the test?  

YES!

What should we know about the Rutherford gold foil experiment?

http://micro.magnet.fsu.edu/electromag/java/rutherford/

“What they found, to great surprise, was that while most of the alpha particles passed straight through the foil, a small percentage of them were deflected at very large angles and some were even backscattered. Because alpha particles have about 8000 times the mass of an electron and impacted the foil at very high velocities, it was clear that very strong forces were necessary to deflect and backscatter these particles. Rutherford explained this phenomenon with a revitalized model of the atom in which most of the mass was concentrated into a compact nucleus (holding all of the positive charge), with electrons occupying the bulk of the atom's space and orbiting the nucleus at a distance. With the atom being composed largely of empty space, it was then very easy to construct a scenario where most of the alpha particles passed through the foil, and only the ones that encountered a direct collision with a gold nucleus were deflected or scattered backwards.

What is the Bohr orbit? The Bohr orbit was the suggestion that electrons travel in orbital rings around the nucleus - it was useful to conceive of the idea of energy levels, but not an accurate representation of the geometry or three-dimensional spaces that the electrons actually occupy - these are better captured by the energy sub-levels and orbitals or the s, p, d, and f shapes.

How do you make a valence energy level diagrams and are there ever d orbitals in it? (See question below about VALENCE meaning for different atoms)

What does it mean for an electron to have a spin? what did we do with that?

Electrons motion creates magnetic fields that can be represented as a property called spin.

We used spin to understand the “Pauli Exclusion Principle” - the idea that each orbital can hold up to (but no more than) 2 electrons. The S orbital holds two total. The p sublevel has three orbitals px, py, pz. Since each can hold an electron with each kind of spin, then the p block total can hold 2+2+2 = 6 total electrons.

How does the formula of an ionic compound indicate the ratio of the ionic substance.

Very important. The ions combine in a ratio that reflects how many cations are needed with how many anions to create an overall neutral compound. a single 2+ ion will need two 1- ions to offset it, hence Mg2+ combines with two Cl- to create MgCl2, magnesium chloride.... See also Scandium sulfide example below.

What is the mass of a proton or a neutron and how does it compare to an electron’s mass?

We didn’t give these specific values but we did say an electron is tiny compared to a proton or neutron - here are masses:

electron mass = 9.10938188 × 10-31 kg

proton mass = 1.6726 x 10-27 kg

neutron mass = 1.6749 x 10-27 kg

Importantly, the mass of an electron is only about 1 /2000th the mass of a proton or neutron. By this thinking, we see that the nucleus contains about 99.9% of the mass of an atom but only a tiny tiny fraction of its volume or space. A tiny dense speck in a sea of emptiness.

Do elements in Group IVA (Carbon, for example) form ionic bonds? In general, Carbon and Silicon (Group IVA) do not form ionic bonds, but rather bond covalently. Higher mass elements in Group IVa begin to behave differently (Tin for example) because they are metals

What exactly is an ionic bond how does it differ from a covalent bond? in what ways are they related? IONIC bond is an a electrostatic attraction between a +atom (cation) and a - atom (anion). In an ionic bond one atom has completely taken one (or more) electron from some source to become negatively charged, and another atom has completely lost one (or more) electrons to become positively charged. Covalent bond is about sharing. An electron from each atom is contributed to the shared pair of electrons that is being held in the valence shell of both atoms at the same time. Both bonds hold atoms together, but they mechanisms and behavior of them are a bit different. Ionic bonds can dissolve in water. Covalent bonds generally do not. Salt falls apart in water to free Na+ and Cl- ions. Sugar can dissolve in water, but it does not fall part into pieces.  

How can we determine what type of ion an element will form? what about those elements that are “in between”, like carbon? What happens to them instead? Carbon does not form ions. Other elements lose or gain electrons to fill the outer shell just beyond or just before their natural state. So Ca calcium will lose two electrons to take the shortest path to a filled outer shell, whereas oxygen will gain two electrons to take the shortest path to a filled outer shell.

Is ‘reactants’ going to be part of this test? Did we cover it this unit? Reactant just means something that can react. Not really important for this test. It was an idea in the Iron -Copper lab (reactants and products)

Could you explain how to do electron configs.  Need to be able to walk up the periodic table knowing the energy levels and the named blocks - there’s really only one electron configuration to learn - it’s then just a question of how far up this pattern to go for a given element. For example, there’s just one alphabet for us: ABCDEFGHIJKLMNOPQRSTUVWXYZ but if I say so give me the first twelve letters, you would just say, oh that’s ABCDEFGHIJKL.

electron configuration is just 1s2-2s2-2p6-3s2-3p6-4s2-3d10-4p6-5s2-4d10-5p6-6s2-4f14-5d10-6p6-7s2-5f14-6d10-7p6...

so if I say ok so I have an element with 14 electrons, what is its electron config, its just

1s2-2s2-2p6-3s2-3p2.

What’s the difference between molecules vs. ions vs. salts? Molecule is atoms covalently bonded (water, H2O, carbon dioxide, CO2, methane CHt4). Ions are charged atoms (Ca2+, F-, O2-) that combine together to form ionic compounds (NaF, sodium fluoride for example) that are called salts.

How do you solve an ionic compound problem? EX: Scandium ion and sulfur ion, what is the compound that will form? START by what ion does each element form.

Scandium - Sc 3+ (right? WHY!) Sulfur forms sulfide ion S2- (right ? WHY!) Then these need to combine into a combine where each will be present in mulitples that fully offesets or balances out the charge of the other. IN other words, if its Na+ and Cl- it’s just one to one NaCl. If it is Li+ and O2- it must be two LIthiums for every oxide, or Li2O. With the Sc and S it must be two scandiums (6+) to three sulfides (6-) or the formula Sc2S3.

How do you know what levels to write in the Valence orbital diagram with the arrows?

On a valence homework, I told you - “give me all electrons beyond Argon.... It’s not wrong to show ALL the electrons, just not necessary. In general, valence electrons means highest energy level  S  & P electrons. For metals in the d block, the Valence story is a little more complicated, because we begin to think about 4s, 3d and 4p - don’t worry about what defines “valence” for the d-block elements.

What does it mean when an element is ionized? It gains or loses electrons to get a filled outer shell and becomes charged - it becomes an ion.

Do we have to know how to draw and explain orbitals? You should know that s-orbital is a sphere, you should know and recognize p-orbitals as bi-lobed set of three. You should be able to sketch those. You do not need to know the specific shapes of the five d-orbitals but you should know that there are five of them!

How does the formula of ionic compound indicate the ratio of ions in the substance?

NaCl is a 1:1 ratio of Na+ to Cl- MgO is also a 1:1 ratio of Mg2+ to O2-. But Na2S is a 2:1 ratio of Na+ to S2-

How can we tell/make an educated guess about what isotope of an atom is the most common without doing any math? Something about the mass number of that isotope...? We just look at the atomic mass on the periodic table and round it to the nearest whole number. Since carbon atomic mass on the PT is 12.011, we can guess that the most common isotope of carbon is 12-C or carbon-12. It is.

What is NaCl? In what ratio would you expect calcium to combine with chlorine to form an ionic compound? What about Scandium and sulfur ? How do you name these compounds. SEE ANSWER ABOVE

What defines the valence electrons? How exactly do you find them? SEE ANSWER ABOVE

For Lewis Dot Structures how do you know what to do with the unshared pairs? You don’t really need to do anything with them,  but you definitely need to know if they are there or not. Oxygen comes with 6 valence electrons, makes two covalent bonds, and after bonding still has two unshared pairs that need to be included in a Lewis Dot structure. Nitrogen has one unshared pair. Fluorine and Chlorine have three unshared pairs.

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These  topics below on building molecules from chemical structures will be reserved for a quiz a little later as we will not yet have had enough practice to include them on the May 3-4 test:

Do we need to know how to build a molecule from a chemical formula ? if so, exactly what would we need to know? (May not reach this point for blocks 4 and 5)

Yes, we need to know how to take a formula like C2H6O and build a correct possible structure and then turn that “stick structure” into a full electron dot structure. First you need to know (or deduce form periodic table) the number of bonds elements form: C- 4 bonds, N- 3 bonds, O- 2 bonds, H- 1 bond, Cl - 1 bond, F- 1 bond. Then we fit them together (like a puzzle) so all atoms are making all the right bonds. We might need a double bond somewhere. Finally, we convert to electron dot structure by trading a stick out for two “dots” (electrons in the covalent bond and then adding in unshared pairs (non bonding electrons)  - 1 pair for nitrogen, 2 pair for oxygen and 3 pair for chlorine, fluorine, etc…..

What’s the difference between the chemical formula and the structural formula? How do you apply these to the order of stick structures?

Chemical formula - C2H6O. Structural formula for same ethanol, CH3CH2OH. Structural formula is telling you more about how the atoms are joined together in units. The structural formula makes it much easier to know how to draw the stick structure that joins the atoms together correctly.

How to determine what warrants double/triple bond? Whatever is needed to allow all the atoms to make the number of bonds they need to make. H makes 1 O makes 2 N makes 3 C makes 4, Cl, F, Br make 1. I have a molecule HCN, hydrogen cyanide. H makes only one bond. C and N MUST be joined by a triple bond to allow C to be making 4 bonds and N to be making 3.

Do you have any suggestions for beginning Lewis Dot Structures? Octet rule and check this out:

http://www.kentchemistry.com/links/AtomicStructure/lewis%20Dots.htm

http://www.chem.ufl.edu/~itl/4411/lectures/14_1fig.gif

How do we show unshared pairs in stick structure? Don’t need to.

Does oxygen always have one unshared pair or? TWO unshared pairs.

On the website you just posted it says when dotting in the Lewis dot structure you put one and two on the same side before going around with the rest but in class you said to go around, which is correct? I think it is showing what we did. It just isn’t drawing vacancies. look at Nitrogen. There’s one shared pair together , then the other three are spread around so that each would have a vacancy next to it to allow for covalent bonding. Same thing I showed, I just drew empty boxes in for the vacancies. They aren’t showing the vacancies..

What is a dipole? Di (two) Pole (opposite ends) - a bond or a molecule that has opposite charges at the opposing ends or sides of the bond or molecule. As a molecule, water has a dipole nature. The C-O bond also is a dipole because of the electronegativity difference between carbon and oxygen.