Answer:
21. Most metals are brittle.
22. increases from top to bottom within the group
23. Neon is the most stable element because its highest occupied energy level is filled.
24. transfer of electrons
25. electrons are not shared equally between atoms
26. BeCl2
27. double-replacement and decomposition
28. exothermic
29. The reaction rate decreases.
30. The salt dissolved most quickly in the warm water.
31. saturated
32. feels slippery
33. hydroxide ions in solution
34. stay about the same
35-40. I do not know.
41. a bee hovering around a bee hive
42. the number of valence electrons in atoms of the element
Explanation:
21. Metals are ductile and malleable (conveniently also characteristics for chewing gum). They are stretchy and squishy. Brittle is the opposite of stretchy and squishy, and is a characteristic of non-metals.
22. On the periodic table, elements higher up are safer to use in labs. They are safer because they are less likely to react with other substances. Therefore the tendency to react with other substances increases from top to bottom within the group.
23. "Noble gases stable" (periodic table song by ASAP Science). Neon is a noble gas, therefore it is stable. When elements have only one electron to gain or lose, they are very reactive or least stable.
24. The formation of an ionic bond (metal + non-metal) is caused by the giving and receiving of electrons. Neutrons and protons do not transfer. Electrons are shared in covalent/molecular bonds (between non-metals).
25. A polar covalent bond occurs between non-metals, therefore they share electrons (ionic bonds transfer electrons). Non-metals become anions (whereas metals become cations). Polar bonds have unequal sharing and nonpolar bonds have equal sharing.
26. A one-to-two ratio of beryllium ions to chloride ions means for every Be, there are two Cl. The number of atoms is represented by the ratio, and the numbers of atoms are written as subscripts after the element symbol.
27. MgCO2 reacting with HNO3 to form magnesium nitrate and carbonic acid is a double-replacement reaction. The elements in the beginning substances "switch partners" to form the products.
Carbonic acid then breaks down into water and carbon dioxide is decomposition. This occurs when the elements that make up a compound are split up.
28. In 2Cu + O2 => 2CuO + 315 kJ , the energy is on the right side. The right side is the products, or the stuff that was made. kJ is a unit to measure energy, therefore energy was made. Exothermic is the term that means energy was released.
29. Since oxygen is needed for a fire to burn, decreasing the oxygen slows the reaction rate (the reaction is burning, formally known as combustion).
30. Two things help substances dissolve: heat and stirring. Warm water is hotter than room-temperature water and ice water. This makes the salt dissolve faster.
31. A solution that contains more solute than it would normally hold is saturated. Saturated means there is a more than concentrated amount of solute in the solution. Concentrated is when there is a maximum amount of solute that will dissolve.
32. Acids do not feel slippery -- that is a characteristic of a base. To remember, bases are generally soaps and soaps are slippery. Acids taste sour and bases taste bitter. Both acids and bases change the color of an indicator .
33. A base produces hydroxide ions, represented by OH. The OH is usually at the end of the chemical formula. Acids produce hydrogen ions, generally written at the front of the chemical formula.
34. Adding a little bit of acid to a buffer will cause the pH of the solution to stay about the same, probably increase a little. Buffer solutions are meant to make the pH "buffer". To remember, DVDs used to buffer. It's the same thing as "lag" for phones.
35-40: I'm sorry, I have no answer.
41. Electrons orbit like the plants revolve around the sun. Electrons revolve around a nucleus. A bee hovering around a bee hive is probably flying around it in circles.
42. The tendency of an element to react is closely related to the number of valence electrons in atoms of the element. If the valency is 8, the electron shell is full. The element is stable, opposite to reactive -- this applies to all noble gases (group 8A on the periodic table). If the valency is 1 or 7, the element is very close to being stable but not, the "desire" is so great and makes the element very reactive.