Elements,Compounds, and also Mixtures

Elements Atoms Compounds Characteristics of Compounds
Determining Ionic Vs. Covalent Molecules Mixtures Vs. Compunds


Any substance that includes only one type of one atom is knownas an element. Due to the fact that atoms cannot be created ordestroyed in a keolistravelservices.comistry reaction, facets such as phosphorus (P4)or sulfur (S8) can not be damaged down right into simplersubstances by these reactions.

You are watching: When elements combine to form compounds,

Example: Water decomposes into a mixture that hydrogen andoxygen once an electric existing is passed with the liquid.Hydrogen and also oxygen, on the other hand, can not be decomposed intosimpler substances. They are as such the elementary, orsimplest, keolistravelservices.comistry substances - elements.

Each element is represented by a distinctive symbol. The notationfor each aspect can be uncovered on the regular table the elements.

The aspects can be separated into three categories the havecharacteristic properties: metals, nonmetals, and also semimetals.Most elements are metals, i m sorry are uncovered on the left and towardthe bottom that the periodic table. A handful of nonmetals areclustered in the top right corner of the regular table. Thesemimetals have the right to be discovered along the splitting line between themetals and the nonmetals.


Elements are consisted of of atoms, the smallestparticle that has any of the nature of the element.JohnDalton, in 1803, proposed a contemporary theory the the atom based onthe complying with assumptions.

1. Matter is comprised of atom that space indivisible and indestructible.

2. All atoms of an aspect are identical.

3. Atom of different aspects have different weights and also different keolistravelservices.comical properties.

4. Atom of different facets combine in basic whole numbers to type compounds.

5. Atoms cannot be created or destroyed. When a compound decomposes, the atoms room recovered unchanged.

Go To atoms Vs. Ion


Elements incorporate to kind keolistravelservices.comical compounds that are oftendivided right into two categories.

Metals regularly react v nonmetals to form ionic compounds.These compounds are composed of optimistic and negative ions formedby including or subtracting electron from neutral atom andmolecules.


Nonmetals incorporate with each various other to kind covalentcompounds, i m sorry exist as neutral molecules.


The shorthand notation for a compound describes the number ofatoms of each element, i m sorry is indicated by a subscript writtenafter the symbol because that the element. By convention, no subscript iswritten when a molecule consists of only one atom of one element.Thus, water is H2O and carbon dioxide is CO2.

Characteristics ofIonic and also Covalent Compounds

Ionic Compounds

Covalent Compounds

Contain optimistic and an unfavorable ions (Na+Cl-)

Exist together neutral molecules (C6H12O2)

Solids suchs as table salt (NaCl(s))

Solids, liquids,or gases (C6H12O6(s), H2O(l), CO2(g))

High melting and also boiling points

Lower melting and boiling point out (i.e., regularly exist together a fluid or gas in ~ room temperature)

Strong force of attraction between particles

Relatively weak force of attraction in between molecules

Separate into charged corpuscle in water to give a systems that conducts electricity


Remain as same molecule in water and also will no conduct electricity


Determining if aCompound is Ionic or Covalent

Calculate the difference in between the electronegativities oftwo elements in a compound and the median of theirelectronegativites, and find the intersection the these values onthe figure shown below to assist determine if the link is ionicor covalent, or metallic.


Practice problem 1:

For each of the following compounds, predict even if it is you would suppose it to be ionic or covalent.

(a) chromium(III) oxide, Cr2O3

(b) carbon tetrachloride, CCl4

(c) methanol, CH3OH

(d) strontium fluoride, SrF2

Click here to check your answer come Practice problem 1

Practice problem 2:

Use the following data to suggest a means of distinguishing between ionic and covalent compounds.

Melting point ( oC) Boiling allude ( oC)
Cr2O3 2266 4000
SrF2 1470 2489
CCl4 -22.9 76.6
CH3OH -97.8 64.7

Click below to check your answer to Practice trouble 2

Practice trouble 3:

Which that the following compounds must conduct one electric present when dissolved in water?

(a) methanol, CH3OH

(b) strontium fluoride, SrF2

Click right here to examine your answer come Practice problem 3


A molecule is the smallest fragment that has any of theproperties that a compound. The formula for a molecule need to beneutral. As soon as writing the formula for an ionic compound, thecharges top top the ions have to balance, the number of postive chargesmust equal the number of negative charges.


CaCl2 Balanced formula has actually 2 hopeful charges (1 calcium ion with +2 charge) and 2 an unfavorable charges (2 chloride ions through a -1 charge)
Al2(SO4)3 Balanced formula has actually 6 confident charges (2 aluminum ions through a +3 charge) and also 6 negative charges (3 sulfate ions through -2 charge)

Mixtures Vs. Compounds

The law of consistent composition claims thatthe ratio by mass of the aspects in a keolistravelservices.comical compound isalways the same, nevertheless of the resource of the compound. Thelaw of constant composition can be offered to differentiate betweencompounds and also mixtures the elements: Compounds have actually aconstant composition; mixtures execute not. Water is always88.8% O and also 11.2% H by load regardless of its source. Brass isan example of a mixture of 2 elements: copper and also zinc. It cancontain as little as 10%, or as much as 45%, zinc.

Another difference in between compounds and also mixtures the elementsis the ease with which the elements can be separated. Mixtures,such as the atmosphere, contain 2 or much more substances the arerelatively straightforward to separate. The individual components of amixture deserve to be physically be separated from each other.

keolistravelservices.comical compound are really different native mixtures: Theelements in a keolistravelservices.comical compound deserve to only be separated bydestroying the compound. Some of the differences in between keolistravelservices.comicalcompounds and also mixtures of aspects are shown by thefollowing example using raisin bran and "Crispix.".

Raisin bran has actually the adhering to characteristic nature of a mixture.

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The grain does not have a constant composition; the ratio of raisins to bran flakes alters from sample come sample. the is easy to physically separate the two "elements," to pick out the raisins, because that example, and eat lock separately.

Crispix has some of the characteristic properties of a compound.

The ratio of rice flakes to corn flakes is constant; it is 1:1 in every sample. there is no method to separate the "elements" without breaking the bonds that hold them together.