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It is easy to say that rocks or iron or metals or glass or diamonds are more dense than water, but it is less easy to say why.
Density is mass per unit volume and mass is determined by the type of particle and volume is determined by how much space it takes up.
A single molecule of water (H2O) has a mass of 18 Atomic Mass units.
As a typical rock, quartz (SiO2) has a mass of 60 atomic mass units, or more than three times greater.
The molecules are no so different in size.
The volume occupied by a water molecule is about 30 cubic Angstroms.
The volume occupied by a quartz molecule is about 37 cubic Angstroms.
The density of water is 1.0 grams per cubic centimeter.
The density of quartz is 2.7 grams per cubic centimeter.
It is not unexpected that more massive atoms and molecules have greater density solids or liquids. Mass is not always the only factor, but an important one.
More detail:The density of a material can be reduced to a statement about the individual particles (atoms or molecules) that make up the material. The mass of the material is equal to the mass of a single constituent particle divided by the volume occupied by the particle within the structure of all the other particles.
For a material like water, and H2O molecule has 2 Hydrogen atoms of 1 amu each and 1 oxygen atom of 16 amu, so 18 amu per molecule. The volume occupied by a molecule in water is about 30 cubic angstroms. quartz has 1 molecule per 37 cubic angstroms. So, the mass of the individual molecules is the overwhelming effect that makes quartz 2.7 grams per cubic centimeter and water 1 gram per cubic centimeter.
Most rocks and glasses and minerals have similarly massive atoms. Feldspar, making up most of the Earth's crust works out to 2.56 grams per cubic centimeter. Metals are even more dense. Iron (56 amu) atoms are larger and more massive with a density of 7.87 grams per cubic centimeter.
Water Calculation:
H2O molecule has 2 Hydrogen atoms of 1 amu (Atomic mass unit) each and 1 oxygen atom of 16 amu, so 18 amu per water molecule.
Calculate the number water molecules in a volume of space.
(1 mole/18 g)*(1000g/kg)*(6.023 x10^23 molecules/mole)*(1,000kg/m^3)*(1 m/10^9 nm)^3= 33.5 molecules/cubic nanometer
The space occupied by one molecule is
1,000A^3/33.5 molecules = 30 cubic angstroms per molecule.
One water molecule is in a volume equal to that of a box that is 3.1 angstroms on a side.
Quartz Calculation:
SiO2 has silicon, 28 amu and 2 oxygens, 16 amu each, so SiO2=60 amu.
Molecules per unit volume with 2.7 grams per cubic centimeter:
(2.7 g / cm^3) * (1 000 000 cm^3 / m^3) * (6 * 10^23 molecules /mole)*(1 mole/60 g) * (1 m^3 / 10^30 A^3) = 0.027 molecules/ A^3= 27 molecules per cubic nanometer.
Volume per quartz molecule is 1 molecule per 37 cubic Angstroms.
End Note:
The density of a material is amazingly difficult to predict based on just knowing the atoms or molecules from which it is made. This is because on needs to know the electronic structure and the bonding involved. Further, the solid forms require the prediction of a crystal structure and the liquid forms require the average distances between molecules that are rather jumbled about. The subject of quantum mechanics is the fundamental theory to predict electronic structure, bonding and molecular forces. Statistical mechanics is needed to predict the bulk properties of a mass of many molecules.
What else can I help you with?
What things don't float in water?
Items with a higher density than water do not float, such as rocks, metals, and most plastics. Additionally, items that are porous and absorb water, like paper or cloth, can become saturated and sink.
Which things float on water and which sinks into it?
Objects that are less dense than water will float on it, such as wood, plastic, cork, and ice. Objects that are more dense than water will sink, such as metals like iron and steel, rocks, and most plastics. The buoyancy of an object is determined by its density compared to the density of water.
Can a brick float?
Objects denser than water will sink; objects less dense than water will float. Since aluminum metal has a density of around 2.7 grams per cubic centimeter and water has a density of 1.0, a solid block of aluminum would sink.
An object most likely sink in water if it has low density?
The lower an objects density the less likely it is to sink in water. Objects with a higher density than water will sink if placed in it while objects with a lower density than water will float if placed in it.
Would a ship will float more in salt water or fresh water?
The more salt in water the more buoyant an object becomes. The salt makes the water more denser. Check out the dead sea. Most salt content in any lake or sea.The density of the salt water is greater than the density of an object. Items sink if their own density is greater than the density of whatever they are trying to float in. Items float to the top if their density is less than the density of what they are floating in, and items hang in the middle if the densities are the same. Adding in the salt gives the water a greater density than the water did had before, so the item doesn't float in freshwater.We call the amount of mass in a given amount of space the density. For instance, we could measure the mass of fresh water (like water from a stream) in a container. We could then determine the density if fresh water. However, if we filled the same container with salt water, it would have more mass because the ocean water has the mass of pure water plus the mass of the salt.Since there is more mass in the same volume, ocean water has a greater density then fresh water.For something to float, it must have a density less than in what it is floating. This means that steam, which is less dense than air, rises (or floats) in the air.It may seem odd that an enormous ship can float when steel is denser than water. However, if you look at the entire ship you see that there are many places filled with things less dense than water, like air. This means that the density of the entire ship is less dense than that of water and it floats.
Does ice have a greater density then a rock?
It depends on the type of rock and the conditions. Generally, ice has a lower density than most rocks, which is why ice floats on water. Rocks vary in density based on their composition and can be denser than ice.
Which has a greater density sir or water?
Most sirs are slightly denser than water. Particularly fat sirs may not be.
What things don't float in water?
Items with a higher density than water do not float, such as rocks, metals, and most plastics. Additionally, items that are porous and absorb water, like paper or cloth, can become saturated and sink.
Which things float on water and which sinks into it?
Objects that are less dense than water will float on it, such as wood, plastic, cork, and ice. Objects that are more dense than water will sink, such as metals like iron and steel, rocks, and most plastics. The buoyancy of an object is determined by its density compared to the density of water.
Do most metals have low density?
No. Most metals have densities greater than that of water, which is 1g/ml.
What is significant about the density of water?
Probably the most significant thing about it from a biological standpoint is that it's greater than that of ice.
Is a coin denser than water?
Yes, most coins are denser than water. The density of water is about 1 gram per cubic centimeter, while the density of most coins, such as copper or silver, is greater than that. This means that a coin will sink in water.
Why don't rocks float?
Rocks are generally denser than water, so they sink instead of floating. The buoyant force acting on an object in water is not sufficient to counterbalance the weight of most rocks, causing them to sink. Additionally, rocks are not porous enough to trap enough air to make them float.
Do people have density?
Yes but to be exact you would need a specific person. Most people have a density of slightly less than 1 because they float in water. If you do not float then your density is slightly greater than 1.
Is a magnet more dense than water?
No, a magnet is not more dense than water. Density is the measure of how much mass is contained in a given volume, and the density of water is greater than that of most metals, including magnets.
Why are there things that don't float on water?
An object's density is related to its weight and size. If the density is less than that of water, it will float on the water. If it is greater than that of water, it will sink. Water is not very dense - most things don't float on water. This is because they are denser than it and it cannot support them.
Can a brick float?
Objects denser than water will sink; objects less dense than water will float. Since aluminum metal has a density of around 2.7 grams per cubic centimeter and water has a density of 1.0, a solid block of aluminum would sink.
