Lesson 21: Chapter 21 Bonding in Metals, Alloys, and Semiconductors

Why are metals opaque? A. because the atoms are closer together than the wavelength of light B. because metals are good conductors C. because metals are malleable D. because metals have high melting and boiling points E. because metals have empty, overlapping orbitals for their electrons

because metals have empty, overlapping orbitals for their electrons

What happens to the spacing between the energy of one MO and the next one immediately above or below it as the number of atoms that come together increases? A. Increases B. Decreases C. Remains the same

decreases

Current can flow in all directions in an LED. A. true B, false

false

Which of the following is NOT why alloys are useful to us today? Alloys A. have lower melting temperatures. B. have a higher conductivity rate. C. are less malleable. D. reduce weight in objects.

have a higher conductivity rate

What are properties of metals?

- high melting/boiling temperature - high density - malleability - electrical conductivity - thermal conductivity - opacity - reflectivity

If GaAs forms a semiconductor like Ge, which of the following elements will form a semiconductor like Si? A. C and Ge B. B and As C. Ga and N D. Al and P

Al and P

LEDs (light emitting diodes)

- formed by a P-type semiconductor being bonded to an N-type semiconductor - current flows in one direction only (from N to P) - as the electrons cross the band gap the electron loses energy and emits a photon

Locate the elements palladium (Pd, atomic #46) and nickel (Ni, atomic #28) on the periodic table. If Pd is combined with Ni, which of the following characteristics will the product show at room temperature? A. Non-conducting, transparent solid. B. Shiny, malleable solid. C. Transparent gas. D. Brittle, opaque solid. E. Opaque gas.

shiny, malleable solid

The diagrams above show how a photon can be emitted from three different semiconductors, one red, one yellow, and one blue. Which emits a red photon? (left is smallest band, middle is in-between, right is biggest band) A. The first B. The second C. The last

the first

When you compare the band gap for a red and a blue LED, what is true? A. The red LED has the smallest band gap. B. The blue LED has the smallest band gap. C. The band gaps are equal as long as the battery powering them is the same. D. The color of light doesn't have anything to do with the band gap.

the red LED has the smallest band gap

Which type of atom has valence electron states high enough in energy that they overlap with the stacked together molecular oribitals that form the conduction band? A. metal B. non-metal

metal

Which type of atom has valence electrons higher in the energy well? A. metal B. non-metal

metal

Which of the following is a correct comparison of metals and semi-conductors? A. Metals have a larger band gap than semi-conductors. B. Metals' resistance increases when temperature increases while a semi-conductors resistance decreases. C. Semi-conductors' molecular orbitals overlap while metals' don't. D. Metals have more valence electrons than semi-conductors. E. Metals have larger electrical resistance than semi-conductors.

metals' resistance increases when temperature increases while a semi-conductors resistance decreases

Which type of atom has the highest ionization energy? A. metal B. non-metal

non-metal

Why are metals malleable?

- electrons serve as a lubricant and allow the layers of the nuclei to slide past one another - the repulsive forces form one nucleus to another are reduced by the mobile electrons

Band Gap

- energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors - gives semiconductors different properties than a metal

Why do metals have high melting/boiling temperatures?

- because there are strong attractive interactions between the nuclei and the sea of electrons - the strong interaction requires more energy to break and temperatures must be higher

Metals have higher ionization energies than non-metals do A. true B. false

false

Semiconductors

- conducts electricity better than insulators but not as good as metals - become better conductors as their temperature increases - found along the staircase of the periodic table - their energy bands are split in two parts w/a portion where there are no orbitals (band gap)

Why are metals opaque?

- due to the existence of the energy band - because of the continuous band of orbitals any visible light photon that hits it will be absorbed

Metallic Bond

- chemical bond that binds metal atoms to other metal atoms in forming metal substances - molecules' orbitals become so closely spaced that they form a band of energy - orbitals are so close they are essentially continuous - form a sea of electrons

Alloy

- combination of two or more metals into a single homogenous substance - changes some of the properties - can be formed from atoms with similar or different diameters - alloys form as the overall energy is lowered and entropy increases - generally not as good of a conductor - melt at lower temperatures - less malleable - weigh lesss

What happens to the number of MO's as the number of atoms that come together increases? A. Increases B. Decreases C. Remains the same

increases