AP CHEMISTRY EXAM QUESTIONS 1

AP CHEMISTRY EXAM QUESTIONS 1

• properties of nanoparticles: - large surface area compared to volume

• small size and unique structure mean they can be used to develop composite (made up of

several parts) nanomaterials.

• When a substance is processed into nanoparticles its physical, chemical and optical

properties change

• nanoparticles interact differently with light (used in sunscreens)

• the nucleus of an atom is approximately -- times smaller than the size of the atom: 10000-

100000

• define elements: materials containing just 1 type of atom. Some non metals form a covalent network lattice. Some non metallic elements are monoatomic which means they exist as individual atoms. They're known as noble gases, as they're unreactive • define compounds: materials containing different types of atoms in fixed ratios. The atoms in compounds can form molecules or large networks of atoms • atomic structure: atoms have a positively charged nucleus surrounded by negatively charged electrons. Within the nucleus, there are 2 particles: protons (positively charged) and neutrons (no charge) • electrons are -- times smaller than a neutron (or neutron): 1800 times smaller than a proton or a neutron • electrostatic attraction: negative attracts positive. Electrons are bound to the nucleus by this force to the protons in the nucleus. The charge of an electron is equal but opposite to the charge of a proton

• define atomic number: number of protons

• define mass number: number of protons and neutrons

• why does the number of protons have to be equal to the number of electrons: the atom is electrically neutral and therefore for it to be neutral there needs to be an equal amount of protons and neutrons • define isotopes: all atoms that belong to the same element have the same number of protons (same atomic number), but not all atoms that belong to the same element have the same mass number • emission spectra: Heating an element can cause an electron to absorb energy and jump to a higher energy state. Shortly afterwards the electron returns to the lower energy state, releasing a fixed amount of energy as light. Electrons may return directly to the ground state or may move to other energy levels before returning to the ground state.

• when atoms are heated, they give off electromagnetic radiation or light. If the light passes 1 / 3

through a prism, it produces a spectrum with a black background and a number of colored lines known as line spectra or emission spectra. Each emission spectrum is unique for a particular element and can be used to identify different elements.• light energies in the emission spectra: violet= high energy, as the colour changes to blue, green, yellow and orange the energy decreases. Red light is the lowest • info from the emission spectra: - atoms of the same element produce identical line spectra

• each element has a unique line and therefor a unique electronic strcuture

• ionisation energy: the energy needed to remove an electron from an atom. The first electron to be removed has the lowest ionisation energy and is therefore the easiest to remove.

• electrons in the same shell: - are about the same distance from the nucleus

-have about the same energy

• max number of electrons in each shell: n1=2 n2=8

n3=18 n4=32 n=2n^2 • octet rule: atoms lose, gain or share valence electrons in order to have a full outer shell

• energy levels within an atom:

• subshell notation: SUBSHELLS: first shell contains only s, second contains s,p and third contains s, p, d and so on.ORBITALS: s has one orbital, p has 3 orbitals, d has 5 orbitals, f has seven orbitals. The total number of orbitals in a shell is given by n^2.

• exceptions to the subshell notation: chromium and copper

• chromium and copper exceptions define: they occur in the transition metals, whose electron configurations allow them special chemical properties such as multiple valence states.This all occurs due to the fact that the 4s and 3d orbitals are extremely close in energy.Usually the 4s orbitals will fill (contains 2 electrons) before the 3d orbital begins to fill. This is not the case in Cu and Cr.CHROMIUM - Having one electron in each of the energetically similar orbitals is more favourable than having the 4s orbitals filled and one of the 3d orbitals left unfilled 1s2 2s2 2p6 3s2 3p6 3d5 4s1

COPPER - Is more stable with a completely full 3d subshell and a partially filled 4s then the other way around 1s2 2s2 2p6 3s2 3p6 3d10 4s1

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SUBSHELLS ARE MORE STABLE EITHER FULL OR HALF FULL

• periodic table blocks:

• periodic table: groups- vertical periods- horizontal

• ionic compound properties: - have a high melting and boiling point

• they're solid at room temperature
• are hard, but brittle, so they're not malleable or ductile
• don't conduct electricity in solid state
• are good conductors of electricity in liquid state or when dissolved in water
• they vary from very soluble to insoluble in water, they're not soluble in non-polar solvents

(oil) • define ionic compounds: made by the chemical combination of metallic and non-metallic elements • nanoscience: the study of nanoparticles and nanotechnology. Nanotechnology is the use of technologies that manipulate and investigate the properties of materials on the nanoscale.• the prefix nano refers to...: refers to one billionth or 10-9 in scientific notations.• cation: metal atoms lose electrons to non metallic atoms and become positively charged metal ions • anions: non metal atoms gain electrons from metal atoms and became negatively charged non metal ions • what forces result from the attraction between positive and negative charges: electrostatic • explain high melting points of ionic compounds: they have high melting points because a large amount of energy is needed to overcome the electrostatic attraction between the oppositely charges ions and allow them to move. So, the ionic bonds between the + and - ions is strong.• explain hardness and brittleness of ionic compounds: a strong force is need- ed to disrupt the crystal lattice, which means that it's very hard. Although a salt crystal is hard, a strong force will shatter the crystal, meaning it's brittle. This is because layers of ions will move relative to each other due to the force of blow. During this movement, ions of like charge shift so they are next to each other. The repulsion between the similarly charged ions causes the crystal to shatter • explain electrical conductivity of ionic compounds: in solid form, ions are held in the crystal lattice and are not free to move, therefore don't conduct electricity. When solids melt, the ions become free to move, enabling the cations and anions in the molten compound to conduct electricity. When they dissolve in water, ionic bonds in the lattice break and the ions are separated and move freely. When an electric current is applied, + ions move towards the - charged electrode and - ions move towards the + charged electrodes • properties of metals: Exhibit a range of melting points and relatively high boiling points

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