Chem Chapter 5 - Elements, Compounds And Mixtures Flashcards
What is an element?
A pure substance that cannot be broken down into two or more simpler substances by chemical methods
When will elements appear as atoms?
If they are not chemically bonded to each other
When will elements appear as molecules?
If they are covalently bonded
What are compounds?
A pure substance containing two or more elements that are chemically combined in a fixed ratio
What do compounds form when chemically bonded?
Covalent compound or ionic compound
Now are compounds separated into their constituents
Chemical methods such as thermal decomposition and electrolysis
How does thermal decomposition separate compounds
Exposing the compound to strong heat
How does electrolysis separate compounds?
Passing an electric current through the compound
What is a mixture
An impure substance containing two Or more compounds and/or elements that are not chemically combined and do not have substances in fixed ratios
Name some physical separation techniques that can be used to separate mixtures
Filtration, chromatography and distillation
Are new substances formed during separation of mixtures?
No new substances are formed
Why do ionic substances have high melting and boiling point
Ions of opposite charges have strong electrostatic forces of attraction between them and a large amount of energy is needed to overcome them. Thus, ionic compounds have high melting and boiling point and are solids at room temperature
Why are ionic substances hard?
Strong electrostatic forces of attraction between opposite charged ions make ionic compounds resistant to deforming and resist motion → hard
What happens when enough force is applied to an ionic compound?
Ions move away from their lattice positions aud ions of same charge approach each other. Repulsive forces between runs of the same change becomes larger than attractive forces and the lattice structure shatters → brittle
Now soluble are ionic compounds?
Soluble in water but are insoluble inorganic solvents
Can ionic compounds conduct electricity in the solid state?
When an ionic compound is in the solid state, the ions in the lattice are only able to vibrate about fixed positions which makes ions immobile and cannot conduct electricity
Can ionic compounds conduct electricity in the liquid state?
When an ionic compound is molten or in aqueous state, the particles conside pass each other and they are mobile, this they can conduct electricity
What are the structural properties of covalent compounds?
Strong covalent bond, molecules held by weak intermolecular forces of attraction and only a small amount of energy is needed to overcome them. Simple covalent substances are usually gases and liquids at room temperature
Why do covalent substances have low melting and boiling point?
The weak intermolecular forces of attraction between molecules can be easily overcome with a small amount of energy. Thus making them volatile. As the molecule gets larger, the melting and boiling points are higher. Intermolecular forces of attraction are higher
How soluble are covalent substances?
Insoluble in water but soluble in organic solvents
Can covalent substances conduct electricity?
No. They do not have any mobile electrons or ions and those electrons are used for bonding and not for sharing and forming ions
What is an alloy?
An alloy is a mixture of a metal with one or more other elements
Are the number of atoms in an alloy known?
Exact number and distribution unknown, only approximate percentage of each element by its mass is known.
What causes alloys to have different properties prom pure metals?
Irregular arrangement of atoms in alloys
Have a difference between alloys and pure metals
Harder and stronger than pure metals
Name and describe two structural properties of metals and alloys
Malleable: when hammered pure metals can be bent or flattered into a thin sheet
Ductile: pulled (into wire) without breaking
Layer of atoms can slide over one another easily when force is applied
Describe the melting and boiling point of metals and alloys
High melting point and boiling point. Solids at room temperature. Alloys do not have a fixed melting point, as they are mixtures that melt over a range of temperatures
Are metals and alloys good conductor of heat?
Good conductors of heat
Why are metals and alloys good electrical conductors?
Metal atoms have valence electrons freely moving throughout the structure
