States of Matter | Chemistry | Visionlearning
Five States of Matter: Condensate, Solid, Liquid, Gas, Plasma a chemical change would build or break the chemical bonds in the water (H2O) molecules. Phases and Classification of Matter . Covalent bonds are formed between two atoms when both have similar tendencies to attract at room temperature, and, in their solid states, they are typically much softer than ionic solids. . Figure 5 shows the relationship between electronegativity difference and bond type. There are many states of matter beyond solids, liquids, and gases, including as a result of various intermolecular forces such as hydrogen bonds, van der.
Atoms and molecules that have relatively small amounts of energy and movement will interact strongly with each other, while those that have relatively high energy will interact only slightly, if even at all, with others.
Atoms that have low energy interact strongly and tend to "lock" in place with respect to other atoms. Thus, collectively, these atoms form a hard substance, what we call a solid.
Atoms that possess high energy will move past each other freely, flying about a room, and forming what we call a gas. As it turns out, there are several known states of matter ; a few of them are detailed below. Individual molecules are locked in position near each other, and cannot move past one another. The atoms or molecules of solids remain in motion.
However, that motion is limited to vibrational energy; individual molecules stay fixed in place and vibrate next to each other. As the temperature of a solid is increased, the amount of vibration increases, but the solid retains its shape and volume because the molecules are locked in place relative to each other.
To view an example of this, click on the animation below which shows the molecular structure of ice crystals. In liquidsmolecules can move past one another and bump into other molecules; however, they remain relatively close to each other like solids.
Often in liquidsintermolecular forces such as the hydrogen bonds shown in the animation below pull molecules together and are quickly broken.
As the temperature of a liquid is increased, the amount of movement of individual molecules increases. As a result, liquids can "flow" to take the shape of their container but they cannot be easily compressed because the molecules are already close together.
Thus, liquids have an undefined shape, but a defined volume. In the example animation below, we see that liquid water is made up of molecules that can freely move past one another, yet remain relatively close in distance to each other. Thus gas molecules have little interaction with each other beyond occasionally bumping into one another. In the gas state, molecules move quickly and are free to move in any direction, spreading out long distances. As the temperature of a gas increases, the amount of movement of individual molecules increases.
Gases expand to fill their containers and have low density. Because individual molecules are widely separated and can move around easily in the gas state, gases can be compressed easily and they have an undefined shape. Solids, liquidsand gases are the most common states of matter that exist on our planet. If you would like to compare the three states to one another, click on the comparison animation below.
Note the differences in molecular motion of water molecules in these three states. Plasmas are formed under conditions of extremely high energyso high, in fact, that molecules are ripped apart and only free atoms exist. More astounding, plasmas have so much energy that the outer electrons are actually ripped off of individual atoms, thus forming a gas of highly energetic, charged ions.
Because the atoms in plasma exist as charged ions, plasmas behave differently than gases, thus representing a fourth state of matter. Plasmas can be commonly seen simply by looking upward; the high energy conditions that exist in stars such as our sun force individual atoms into the plasma state. Gases Other states of matter As we have seen, increasing energy leads to more molecular motion. Conversely, decreasing energy results in less molecular motion.
- Chemical Bonding: The Nature of the Chemical Bond
- States of matter and intermolecular forces
- States of Matter
As a result, one prediction of Kinetic Molecular Theory is that if we continue to decrease the energy measured as temperature of a substance, we will reach a point at which all molecular motion stops.
The temperature at which molecular motion stops is called absolute zero and has been calculated to be While scientists have cooled substances to temperatures close to absolute zerothey have never actually reached absolute zero.
The difficulty with observing a substance at absolute zero is that to "see" the substance, light is needed, and light itself transfers energy to the substance, thus raising the temperature. Despite these challenges, scientists have recently observed a fifth state of matter that only exists at temperatures very close to absolute zero.
Bose-Einstein Condensates represent a fifth state of matter only seen for the first time in The state is named after Satyendra Nath Bose and Albert Einstein who predicted its existence in the s. B-E condensates are gaseous superfluids cooled to temperatures very near absolute zero.
In this weird state, all the atoms of the condensate attain the same quantum-mechanical state and can flow past one another without friction.
However, it was over years before the concept of the combining power of elements was understood in a more modern sense. A tendency or law prevails hereand that, no matter what the characters of the uniting atoms may be, the combining power of the attracting element, if I may be allowed the term, is always satisfied by the same number of these atoms.
But it was two other scientists who performed the most important contemporary research on the concept of bonding. Inthe American scientist Gilbert N. In that paper he outlined a number of important concepts regarding bonding that are still used today as working models of electron arrangement at the atomic level. Most significantly, Lewis developed a theory about bonding based on the number of outer shell, or valenceelectrons in an atom.
He suggested that a chemical bond was formed when two atoms shared a pair of electrons later renamed a covalent bond by Irving Langmuir. His "Lewis dot diagrams" used a pair of dots to represent each shared pair of electrons that made up a covalent bond Figure 2. Lewis dot structures for the elements in the first two periods of the periodic table. The structures are written as the element symbol surrounded by dots that represent the valence electrons.
The octet had been discussed previously by chemists such as John Newland, who felt it was important, but Lewis advanced the theory. Comprehension Checkpoint Lewis based his theory of bonding on a. The theory of quantum mechanics, developed in the first half of the 20th century, had redefined our modern understanding of the atom and so any theory of bonding would be incomplete if it were not consistent with this new theory see our modules Atomic Theory II: Wave-Particle Duality and the Electron for more information.
In it, he linked the physics of quantum mechanics with the chemical nature of the electron interactions that occur when chemical bonds are made.
Pauling further developed a sliding scale of bond type governed by the electronegativity of the atoms participating in the bond. For our purposes we will concentrate on two common types of chemical bondsnamely covalent and ionic bonding. Molecular bonds are formed when constituent atoms come close enough together such that the outer valence electrons of one atom are attracted to the positive nuclear charge of its neighbor.
As the independent atoms approach one another, there are both repulsive forces between the electrons in each atom and between the nuclei of each atomand attractive forces between the positive nuclei and the negative valence electrons. Some constituents require the addition of energycalled the activation energyto overcome the initial repulsive forces.
But at various distances, the atoms experience different attractive and repulsive forces, ultimately finding the ideal separation distance where the electrostatic forces are reduced to a minimum. This minimum represents the most stable position, and the distance between the atoms at this point is known as the bond length. Covalent bonding As the name suggests, covalent bonding involves the sharing co, meaning joint of valence outer shell electrons.
As described previously, the atoms involved in covalent bonding arrange themselves in order to achieve the greatest energetic stability. And the valence electrons are shared — sometimes equally, and sometimes unequally — between neighboring atoms.
Properties of Liquids
The simplest example of covalent bonding occurs when two hydrogen atoms come together to ultimately form a hydrogen moleculeH2 Figure 3. Here the interaction of two gaseous hydrogen atoms is charted showing the potential energy purple line versus the internuclear distance of the atoms in pm, trillionths of a meter.
The observed minimum in potential energy is indicated as the bond length r between the atoms. Since one shared pair of electrons represents one covalent bondthe hydrogen atoms in a hydrogen molecule are held together with what is known as a single covalent bond, and that can be represented with a single line, thus H-H.
Multiple covalent bonds There are many instances where more than one pair of valence electrons are shared between atomsand in these cases multiple covalent bonds are formed. For example, when four electrons are shared two pairsthe bond is called a double covalent bond ; in the case of six electrons being shared three pairs the bond is called a triple covalent bond. Common examples of such multiple bonds are those formed between atoms in oxygen and nitrogen gas.
The bonds between gaseous oxygen and nitrogen atoms.
Double covalent bonds are shorter and stronger than comparable single covalent bondsand in turn, triple bonds are shorter and stronger than double bonds — nitrogen gasfor example, does not react readily because it is a strongly bonded stable compound.
This type of bond is classically described as occurring when atoms interact with one another to either lose or gain electrons. Those atoms that have lost electrons acquire a net positive charge and are called cationsand those that have gained electrons acquire a net negative charge and are referred to as anions.
States of Matter - Atomic Bonding | Interaction Potential | Dipole - PhET Interactive Simulations
In reality even the most classic examples of ionic bondingsuch as the sodium chloride bondcontain characteristics of covalent bonding, or sharing of electrons of outer shell electrons. Elements have no such feelings; rather, the actual reason for bond formation should be considered in terms of the energetic stability arising from the electrostatic interaction of positively charged nuclei with negatively charged electrons. Substances that are held together by ionic bonds like sodium chloride can commonly separate into true charged ions when acted upon by an external forcesuch as when they dissolve in water.
The force of attraction between neighboring atoms gives ionic solids an extremely ordered structure known as an ionic latticewhere the oppositely charged particles line up with one another to create a rigid, strongly bonded structure Figure 5.
A sodium chloride crystal, showing the rigid, highly organized structure. The lattice structure of ionic solids conveys certain properties common to ionic substances. High melting and boiling points due to the strong nature of the ionic bonds throughout the lattice. An inability to conduct electricity in solid form when the ions are held rigidly in fixed positions within the lattice structure. Ionic solids are insulators. However, ionic compounds are often capable of conducting electricity when molten or in solution when the ions are free to move.
An ability to dissolve in polar solvents such as water, whose partially charged nature leads to an attraction to the oppositely charged ions in the lattice. The special properties of ionic solids are discussed in further detail in the module Properties of Solids. Comprehension Checkpoint Atoms that lose electrons and acquire a net positive charge and are called a. Lewis dot diagrams Lewis used dots to represent valence electrons.
Lewis dot diagrams see Figure 1 are a quick and easy way to show the valence electron configuration of individual atoms where no bonds have yet been made. The dot diagrams can also be used to represent the molecules that are formed when different species bond with one another. In the case of molecules, dots are placed between two atoms to depict covalent bondswhere two dots a shared pair of electrons denote a single covalent bond. In the case of the hydrogen molecule discussed above, the two dots in the Lewis diagram represent a single pair of shared electrons and thus a single bond Figure 6.
Two hydrogen atoms are connected by a covalent bond. This can be represented by two dots left or a single bar right. When is it ionic?