Question

A) list and give example of the 5 unifying themes of biology

B) List 3 types of chemical bonds and give an example substance or compound that possesses the type of bonding

C) How many electrons does Fluorine have? how many electron shells would fluorine have based on it's number of electrons? how many actual electrons would fill the valence shell of fluorine?

Answer 1

Q a) Unifying themes are the characteristics which differentiates living organisms from their non- living counterparts or these are the general properties of living organisms which separates them from non-living things.

The five unifying themes of biology are

1) Cell structure and function

2) Stability and homeostasis

3) Reproduction and inheritance

4) Evolution

5) Interdependence of organisms.

1) Cell structure and function:-

Cell is the basic unit of structure and function of an organism or living being, all organisms are made up of either a single cell called unicellular or many cells called multicellular. Cells contain specific structures for various functions they are called organelles. There are various types of cells but they have certain basic similarities they are they are surrounded by cell membrane in animal cells and by cell wall in plant cells contain cytoplasm, have DNA as the genetic material (which transfers genetic information from parent cell to offspring), cells undergo either asexual or sexual reproduction to produce new cells.

2) Stability and homeostasis:-

Usually all organism maintain a stable internal condition that is their body temperature and water content, show homeostasis that is inspite of changes in the outer environment they maintain their internal condition stable.

3) Reproduction and inheritance:-

All organisms produce individuals of their own kind, by transmitting hereditary materials in the form of DNA to their offspring. In unicellular organisms like bacteria DNA is in the form of a single circular form in cytoplasm, in multicellular organisms they are double stranded and found inside nucleus, DNA contains short segments called genes which carry the information for various characteristics of an organism, and get transferred to offspring by which the characteristics of parent are inherited to the offspring.

4) Evolution:-

In a population the characteristics do change after certain generations that is called evolution, or in other words the changes in the organism over a long period of time is called evolution.

Natural selection or survival of the fittest is the process by which evolution takes place. Organisms having appropriate characters according to the changing environment are able to survive. Competition for resources like food, habitat, mate etc. causes evolution.

5) Interdependence of organisms:-

All organisms living in a biotic community are dependent on other organism as well as on the environment, that is on biotic and abiotic factors, the living things are called biotic factors (plants, animals, microorganisms) and the non-living things are called abiotic factors (soil, water, sunlight etc. are called the abiotic factors).

These are the various unifying themes of biology and their example.

Qb) chemical compounds are formed by joining of two or more atoms, there are three types of bonds which help in joining the atoms they are (i) covalent bond (ii) ionic bond (iii) metallic bonds

(i)Covalent bond:- In covalent bond there is sharing of a pair of valence electrons by two atoms,

Example- in case of chlorine two chlorine atoms can attain a stable structure by sharing their single unpaired electron by which a covalent bond is formed between them. In this both the atoms have tendency to attract electrons and neither has a tendency to donate electron so they share the electrons to get the octet configuration and become more stable.

(ii)Ionic bond:-

In this case there is complete transfer of valence electrons between atoms, it is a type of chemical bond which produces two opposite charge ions. In this a metal loses an electron to become a positively charged cation and a non-metal accepts the electron to become a negatively charged ion called anion. In ionic bind there is an electron donor which is a metal and an electron acceptor which is a non-metal. Metals loose electron because usually they have few electrons in their outermost shell and usually non-metals have electrons near to 8 electrons in their valence shell or outermost shell, so they accept electron and attain the octet rule. In ionic bond the net charge of the compound should be zero.

Example:- in case of Nacl

Sodium atom donates one electron present in its valence shell to chlorine atom, this produces a Na cation and chlorine anion and the net charge becomes zero.

(iii)Metallic bonding:-

Metallic binding takes place between metals, this is a strong bond which joins many metal atoms together.

Example- in case of sodium the electronic configuration is 1S²2S² 2P⁶ 3S¹, when sodium atoms come together, the electrons in the 3S orbital of sodium atom share the space with neighbouring sodium atom and form a molecular orbital, it is similar to the covalent bond but here the difference is each sodium atom is surrounded by eight other sodium atoms and they are again surrounded or touched by another 8 sodium atoms, here all the 3S orbitals overlap to form many molecular orbitals and the electrons can move freely between these orbitals by which they become detached from their original or parent atom, and these electrons are called delocalized electrons. The metal is held together by the strong force of attraction between positive nuclei and the delocalized electrons. This is called metallic binding.

Q c) Answer-

Fluorine has 9 electrons in it, as its atomic number is 9, it is known that the number of electrons of an atom is equal to the atomic number of the atom.

It has 9 electrons, 9 protons and 10 neutrons in it.

Based on its number of electrons it has two shells, first shell contains two electrons and second shell contains 7 electrons.

It has a valence of 1 and its valence shell contains 7 electrons , it can take one electron to satisfy the octet rule. By taking one electron its valence shell will contain 8 electrons satisfying the octet rule. So 1 electron will fill the valence shell of fluorine.