Study guide for science chapter 5 test

What is the atomic number of calcium?

20

If a reaction occurs between potassium(k) and oxygen(o), what will be the ratio of potassium ions to oxide ions in the resulting compound, potassium oxide?

2:1

A carbon atom can form 4 covalent bonds. How many valence electrons does it have?

4 valence electrons.

Magnesium chloride is an example of an ionic compound, which means....

A compound composed of positive and negative ions.

Pure metals tend to be weaker and more reactive than an alloy, which is...

A mixture made of two or more elements, at least one in which is a metal.

A covalent bond in which electrons are shared unequally is....

A polar bond

Compare and contrast the general properties of alloys and pure metals.

Alloys can retain many of the physical properties of metals. Gold jewelry and coins are made of an alloy of gold mixed with a harder element, such as copper or silver. Gold alloys are harder than pure gold, but still retain their beauty and shine. Even after thousands of years, objects made of gold alloys still look exactly the same as when they were first made. Iron objects rust so it is often alloyed with one or more elements to make steel.

What is an ion?

An atom or group of atoms that have an elelctric charge.

Which element is less reactive, an element whose atoms have 7 valence electrons or ones with valence electrons?

An element whose atoms have 8 valence electrons because it is stable already and doesn't need any more electrons.

How is the formation of an ionic bond different than the formation of a covalent bond?

An ionic bond forms as a result of an attraction between oppositely charged ions. A covalent bond forms when two atoms share one or more pairs of electrons.

How does a metallic bond differ from an ionic bond?

An ionic bond is the attraction between two oppositely charged ions, positive and negative. A metallic bond is just the attraction between the same metal ions, positive, and the electrons surrounding it.

Which element is the least likely to react with other elements?

Argon because it is stable and has 8 valence electrons.

Why do the properties of elements change in a regular way across a period?

Because as the group numbers increase, the elements become more stable.

Why is the covalent bond between two atoms of the same element a non-polar bond?

Because each atom exerts the same pull on the shared electrons.

Why is it safer to use a nonmetal mixing spoon when cooking something on a stove?

Because metals conduct heat easily because of the valence electron's freedom of motion within a metal.

Why does a metal horseshoe bend but not break when a blacksmith pounds it into shape.

Because the horseshoe is metal, pounding causes the positive metal ions to change position, but the metallic bonds between the ions and the freely moving valence electrons keep the metal ions from breaking apart.

Why do ionic compounds generally have high melting points?

Because they require a lot of energy to break their bonds.

Many molecular compounds with small molecules are gases at room temperature. Water, however, is a liquid. Use what you know about polar and non-polar molecules to explain this difference.

Because water is polar, water molecules have positive and negative ends. This causes water molecules to be attracted to one another and form a liquid at room temperature. Non polar molecules, lacking this type of attraction, can move farther apart and form a gas at room temperature.

Boron is directly above aluminum on the periodic table. Is this statement true?

Boron is in the same group as aluminum and has three valence electrons.

Write the formula for calcium chloride. Explain how you determined the formula.

CaCl2

Write the formula for calcium chloride. Explain how you determined this formula.

CaCl2.

Both carbon dioxide molecules and water molecules have polar bonds. Why then is carbon dioxide a nonpolar molecule while water is a polar molecule?

Carbon dioxide is a non-polar molecule because a carbon dioxide molecule has a straight-line shape. As a result, the two oxygen atoms pull with equal strength in opposite directions. The attractions cancel out, making the molecule non-polar. In contrast, a water molecule, with its two polar bonds, is itself polar. A water molecule has two hydrogen atoms at one end and an oxygen at the other end. The oxygen atoms attract electrons more strongly than the hydrogen atoms so the oxygen ends up having a slight negativd charge and the hydrogen has a slight positive charge. Also, polar bonds are a covalent bond when electrons are shared unequally. Non-polar is when electrons are shared equally.

In a crystal of solid chloride, each sodium ion is attracted to the...

Chloride ions surrounding it.

How are the properties of molecular compounds different from those of ionic compounds?

Compared to ionic compounds, molecular compounds generally have lower melting points. And unlike ionic compounds, molecular compounds do not conduct electric currents when melted or dissolved in water.

What type of bond forms when two atoms of nitrogen join to form a nitrogen molecule? When two atoms of oxygen join to form an oxygen molecule?

Covalent bonds form in both cases. A triple bond forms when two atoms of nitrogen join, and a double bond forms when two atoms of oxygen form.

What information does the organization of the periodic table tell you about how reactive an element may be?

Elements in the same group have the same number of valence electrons in their atoms, and the number of valence electrons determines how much the element will react. The reactivity of metals decreases from left to right across the periodic table.

Valence electrons in an atom are those that are....

Held most loosely

Predict whether carbon dioxide or water would have a higher boiling point. Explain your prediction in terms of the attractions between molecules.

I think water because there is little attraction between non-polar molecules, and carbon dioxide is non-polar. Also, the negatively charged oxygen ends of the polar water molecules attract the positively charged hydrogen ends of the nearby water molecules, whoch causes the attractions to pull the water molecules closer together, which could affect them and make them more reactive to boiling.

When an atom looses or gains electrons, it becomes an....

Ion

What is an alloy?

Is a mixture made of 2 or more elements, at least one in which is a metal. They are generally stronger and less reactive than pure metals from which they are made.

What is a metallic bond?

Is an attraction between a positive metal ion and the many electrons surrounding it.

Summarize how the periodic table is organized, and tell why this organization is useful.

It is organized by the number of valence electrons an element will have and is useful because you can easily find if the element is stable.

What information is given by the formula of an ionic compoud?

It tells you the ratio of an elements ions to another elements ions.

How many valence electrons are in potassium, calcium, Aluminum, oxygen, and iodine. The. Write formulas for the compounds: potassium iodine, calcium oxide, aluminum iodine, and potassium oxide.

K=1 o=6 ca=2 Al=3 I=7. KI, CaO, AlI3, K2O

Which element is most likely to lose two electrons and form an ion with a charge of 2+?

Magnesium(mg)

Explain how metal atoms form metallic bonds. What role do valence electrons play?

Metal atoms combine in regular patterns in which the valence electrons are free to move from atom to atom. Most metals are crystalline solids. Within each crystal, the metal atoms are closely packed and are positively charged ions. Each metal ion is held in place by a metallic bond. The positively charged ions are embedded in a "sea" of valence electrons. The more valence electrons an atom can add to the "sea," the stronger the metallic bond will be.

The metal atoms in stainless steel are held together by....

Metallic bonds

Polyatomic ions such as ammonium ions(NH4-) and nitrate ions(NO3-) are ions that consist of...

More than one atom

Name 4 properties of metals. What accounts for these properties?

Most metals are flexible and can reshape easily. They can be stretched, pushed, or compressed into different shapes without breaking. They are also ductile and can be easily bent and pulled into thin strands or wires. They are also malleable and can be formed into shapes. Metals act flexible because the positive ions are attracted to the loose electrons rather than other metal ions. 3 OTHER PROPERTIES ARE LUSTER, ELECTRICAL CONDUCTIVITY, AND THERMAL CONDUCTIVITY.

Why are most molecular compounds poor conductors?

Most molecular compounds do not conduct electric current. No charged particles are available to move so there is no current.

The formulas N2, H2O, and CO2 all represent molecules, which are...

Neutral particles made of two or more atoms joined by a covalent bond.

Which element would react with two atoms of sodium to form an ionic compound?

Oxygen because an oxide ion has a charge of 2- and needs 2 sodium ions, each with a charge of 1, to cancel that out.

Do oxygen atoms become more or less stable when oxygen forms compounds?

Oxygen would become more stable because it is gaining valence electrons it needs from another element.

Which element can become stable by loosing one electron? Explain.

Sodium can become stable by loosing an electron because it will end up with 8 valence electrons.

How do some atoms in covalent bonds become slightly negative or slightly positive? What type of covalent bonds do these atoms form?

Some become slightly positive or slightly negative because some of the atoms in the elements pull more strongly or share electrons than do atoms of other elements. As a result, the electrons are shared unequally. This is a polar bond and is covalent.

From what pure metals is staineless steal made?

Stainless steal is made from iron, carbon, nickel, and chromium.

An ice cube(solid H2O) and a scoop of table salt(NaCl) are left outside on a warm, sunny day. Does this statement make sense on why the ice cube melted and salt didn't?

The attractive forces between molecules of H2O are much weaker than those between ions in NaCl.

What is the attraction that holds two covalently bonded atoms together?

The force of attraction that holds two atoms together as a result of the rearangement of electrons between them.

When atoms react, they form a chemical bond, which is....

The force of attraction that holds two atoms together as a result of the rearrangement of atoms between them.

What role do valence electrons play in the formation of compounds from elements?

The number of valence electrons determine how many electrons an atom will gain or lose when it forms a compound with another element.

Contrast sodium and chloride ions, including how they form. Write the symbol for each ion.

The sodium ions are positive because they loose an electron when they are formed, whereas chloride atoms are negative because they gain an electron. Cl- and Na

Explain how metallic bonding causes metals to conduct electric current.

The valence electrons in the metals are only loosely held by the positively charged ions, allowing them to move freely among the ions and conduct electricity.

The formula for sulfuric acid is H2SO4. How many atoms of hydrogen, sulfur, and oxygen are in one molecule of sulfuric acid?

There are 2 hydrogen atoms, one atom of sulfur, and 4 oxygen atoms.

In a lightbulb, a thin tungsten wire filament that is wound in a coil conducts electric current. Describe two properties of the metal tungsten that make it a good material for the filament.

There are metal strips on a circuit board and they conduct electric current throughout the circuit. Also, when conducted, electric current flows into the metal at one point and out at another point.

When nitrogen and hydrogen combine, what will be the ratio of hydrogen atoms to nitrogen atoms in a molecule of the resulting compound? Explain.

There will be 3 hydrogen atoms in every 1 nitrogen atom because this combination gives nitrogen 8 valence electrons and hydrogen 2.

What are valence electrons?

They are electrons in the outer shell of an atom and are farthest away from the nucleus and held most loosly

List three properties of ionic compounds.

They are hard and brittle because of the strength of their ionic bonds. Because of their strength, a lot of energy is needed to break their bonds and because of this they have a high melting point. Also, ions in solid crystals are tightly bond to eachother and can't conduct electricity well.

What holds the ions together in sodium chloride? Indicate the specific charges involved.

They are held together by an attractive force called an ionic bond. This is because one is negative and one is positive.

Explain the reactivity of the inert gases in terms of valence electrons.

They are the least reactive elements on the periodic table because they have an exact number or 8 electrons on the table, which means the element will be stable.

Oxygen has 6 valence electrons, as indicated by the 6 dots around the letter symbol "O." Based on this information, how many covalent bonds could an oxygen atom form?

Two

An electron dot diagram shows an atoms number of...

Valence electrons

What is a double bond? Explain how carbon dioxide molecule has a stable set of 8 valence electrons for each atom.

When two atoms share two pairs of electrons. The carbon dioxide atoms has 2 valence electrons that are from carbon and 6 from oxygen, which forms 8 valence electrons and is stable.